Sinterable separation material in additive manufacturing

ABSTRACT

According to one aspect, embodiments of the invention provide a method of 3D printing, comprising depositing a model material in successive layers to form a part, the model material being a metal composite including greater than 50% by volume metal powder and less than 50% by volume a first removable binder, depositing the model material in successive layers to form a support structure adjacent the part, depositing a sinterable separation material between a surface of the part and a surface of the support structure, the sinterable separation material formed from 10-40% by volume ceramic powder and greater than 50% by volume a second removable binder, debinding the first removable binder of the model material and the second removable binder of the sinterable separation material, and sintering the part, the support structure, and the sinterable separation material at a temperature profile that sinters the model material and the sinterable separation material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/419,776 filed on May 22, 2019, entitled “SINTERABLE SEPARATIONMATERIAL IN ADDITIVE MANUFACTURING”, the disclosure of which is hereinincorporated by reference in its entirety.

U.S. patent application Ser. No. 16/419,776 [now U.S. Pat. No.10,800,108] claims the benefit under 35 U.S.C. § 119(e) of U.S.provisional application Ser. No. 62/675,063 filed May 22, 2018, entitled“CERAMIC SEPARATION MATERIAL AND METHODS OF APPLICATION FOR ADDITIVELYMANUFACTURED PARTS” [Expired]; 62/688,273 filed Jun. 21, 2018, entitled“SINTERING CERAMIC SEPARATION MATERIAL AND METHODS OF APPLICATION FORADDITIVELY MANUFACTURED PARTS” [Expired]; 62/688,345 filed Jun. 21, 2018entitled “SINTERING CERAMIC SEPARATION IN ADDITIVE MANUFACTURING”[Expired]; and 62/693,420 filed Jul. 2, 2018 entitled “SINTERINGSEPARATION AND SUPPORT IN ADDITIVE MANUFACTURING” [Expired], thedisclosures of which are herein incorporated by reference in theirentireties. U.S. patent application Ser. No. 16/419,776 is also acontinuation-in-part of each of U.S. patent application Ser. No.16/044,698 filed on Jul. 25, 2018, entitled “SUPPORTS FOR SINTERINGADDITIVELY MANUFACTURED PARTS” [now U.S. Pat. No. 10,377,082] and Ser.No. 15/976,009 filed on May 10, 2018, entitled “RAPID DEBINDING VIAINTERNAL FLUID CHANNELS” [now U.S. Pat. No. 10,464,131], the disclosuresof which are herein incorporated by reference in their entireties.

U.S. patent application Ser. No. 16/044,698 is a continuation of U.S.patent application Ser. No. 15/892,726, filed Feb. 9, 2018, entitled“SUPPORTS FOR SINTERING ADDITIVELY MANUFACTURED PARTS” [now U.S. Pat.No. 10,035,298], which is a continuation of U.S. patent application Ser.No. 15/722,445, filed Oct. 2, 2017, entitled “SUPPORTS FOR SINTERINGADDITIVELY MANUFACTURED PARTS” [now U.S. Pat. No. 10,000,011]. U.S.patent application Ser. No. 15/722,445 claims the benefit under 35U.S.C. § 119(e) of U.S. provisional application Ser. No. 62/429,711,filed Dec. 2, 2016, entitled “SUPPORTS FOR SINTERING ADDITIVELYMANUFACTURED PARTS” [Expired]; 62/430,902, filed Dec. 6, 2016, entitled“WARM SPOOL FEEDING FOR SINTERING ADDITIVELY MANUFACTURED PARTS”[Expired]; 62/442,395 filed Jan. 4, 2017, entitled “INTEGRATEDDEPOSITION AND DEBINDING OF ADDITIVE LAYERS OF SINTER-READY PARTS”[Expired]; 62/480,331 filed Mar. 31, 2017, entitled “SINTERINGADDITIVELY MANUFACTURED PARTS IN A FLUIDIZED BED” [Expired]; 62/489,410filed Apr. 24, 2017, entitled “SINTERING ADDITIVELY MANUFACTURED PARTSIN MICROWAVE OVEN” [Expired]; 62/505,081 filed May 11, 2017, entitled“RAPID DEBINDING VIA INTERNAL FLUID CHANNELS” [Expired]; 62/519,138filed Jun. 13, 2017, entitled “COMPENSATING FOR BINDER-INTERNAL STRESSESIN SINTERABLE 3D PRINTED PARTS” [Expired]; and 62/545,966 filed Aug. 15,2017, entitled “BUBBLE REMEDIATION IN 3D PRINTING OF METAL POWDER INSOLUBLE BINDER FEEDSTOCK”. Each disclosure referenced in this paragraphis herein incorporated by reference in its entirety.

U.S. patent application Ser. No. 15/976,009 claims the benefit under 35U.S.C. § 119(e) of U.S. provisional application Ser. No. 62/505,081filed May 11, 2017, entitled “RAPID DEBINDING VIA INTERNAL FLUIDCHANNELS” [Expired]; 62/519,138 filed Jun. 13, 2017, entitled“COMPENSATING FOR BINDER-INTERNAL STRESSES IN SINTERABLE 3D PRINTEDPARTS” [Expired]; 62/545,966 filed Aug. 15, 2017, entitled “BUBBLEREMEDIATION IN 3D PRINTING OF METAL POWDER IN SOLUBLE BINDER FEEDSTOCK”[Expired]; and 62/575,219 filed Oct. 20, 2017, entitled “3D PRINTINGINTERNAL FREE SPACE WITH A SINTERABLE POWDER FEEDSTOCK” [Expired], thedisclosures of which are herein incorporated by reference in theirentireties. U.S. patent application Ser. No. 15/976,009 is also acontinuation of each of U.S. patent application Ser. No. 15/829,472filed on Dec. 1, 2017, entitled “SINTERING ADDITIVELY MANUFACTURED PARTSWITH A DENSIFICATION LINKING PLATFORM”; Ser. No. 15/829,486 filed onDec. 1, 2017, entitled “STRESS RELAXATION IN ADDITIVELY MANUFACTUREDPARTS” [now Abandoned]; Ser. No. 15/829,500 filed on Dec. 1, 2017,entitled “ADDITIVELY MANUFACTURED PARTS WITH DEBINDING ACCELERATION”;and Ser. No. 15/831,995 filed on Dec. 5, 2017, entitled “ADDITIVEMANUFACTURING WITH HEAT-FLEXED MATERIAL FEEDING”, the disclosures ofwhich are herein incorporated by reference in their entireties.

FIELD

Aspects relate to three-dimensional printing of composite metal orceramic materials.

BACKGROUND

“Three-dimensional printing” as an art includes various methods forproducing metal parts.

In 3D printing, in general, unsupported spans as well as overhanging orcantilevered portions of a part may require removable and/or solubleand/or dispersing supports underneath to provide a facing surface fordeposition or to resist deformation during post-processing.

SUMMARY

According to a first aspect of the embodiments of the present invention,a method of depositing part layers to form a part in additivemanufacturing may include depositing a part layer of green materialincluding a first binder and a sinterable powder.

A release layer of release material including a second binder and arelease powder is deposited upon the part layer of green material. Aportion of the first binder is debound from the part layer of greenmaterial before depositing a subsequent layer of green material.

Optionally, a plurality of part layers of green material is deposited,and the plurality of part layers of green material is debound beforedepositing a subsequent plurality of part layers of green material.

Further optionally, the part layer of green material may be depositedwith a print head, and the portion of the first binder may be debound byimmersing the part in solvent before depositing a subsequent pluralityof part layers of green material. Still further optionally, the partlayer of green material may be deposited with a print head, and theportion of the first binder debound with a debinding head following asame trajectory as the print head.

Alternatively, or in addition, a portion of the first binder is deboundwith a debinding head scanning across a part layer of green material.Following debinding all part layers of green material of the part, theentire part may be sintered.

In another aspect of the embodiments of the present invention, a methodof depositing material for additive manufacturing may include depositinga part layer of green material including a first binder and a sinterablepowder. A portion of the first binder may be debound from the part layerof green material to form a layer of brown material, and a release layerof release material may be deposited including a second binder and arelease powder upon the layer of brown material. A part layer of greenmaterial may be deposited upon the part layer of brown material.

Optionally, following depositing a plurality of part layers of brownmaterial, further the brown material may be further debound. Followingdepositing a plurality of part layers of brown material, the entire partmay be sintered. Following depositing a plurality of part layers ofbrown material, the second binder may be pyrolysed during sintering toleave a loose layer of the release powder.

According to one embodiment, in printing a part using a 3D printingmodel material including a binder and a ceramic or metal sinteringmaterial, a release layer intervenes between support structures and thepart, each of the support structures and the part formed of the modelmaterial or composite. The release layer includes a spherized orpowdered higher melting temperature material—ceramic or high temperaturemetal for example, optionally deposited with a similar (primary) matrixor binder component to the model material. After sintering, the releaselayer may become a loose powder, permitting the supports to be easilyremoved.

In still another aspect of the embodiments of the present invention, anapparatus for additive manufacture of parts may include a sealed chamberin which a part is deposited, and a heated build plate for receiving adeposited part. A print head may deposit part layers of model materialcontaining a binder and a sinterable powder upon the heated build plateand upon prior deposited part layers. A debinding applicator maysubstantially continuously debind the binder from the model material asit is deposited on the heated build plate. A fume extractor may removethe debound binder from the sealed chamber.

Optionally, the fume extractor includes a vacuum pump that maintains thesealed chamber under vacuum.

Alternatively, or in addition, the debinding applicator may include adebinding head that substantially continuously follows a trajectory ofthe print head. A portion of the fume extractor may be transportedtogether with the debinding head to remove debound binder from aposition continuously adjacent the debinding head. The debindingapplicator optionally operates upon one or more part layers, but fewerthan all part layers, at one time. The debinding head may a solventnozzle (such as a spray or drip) that releases debinding fluid upon apart layer of green material, and/or a heat energy projector (such as aheat gun, or a laser) that projects heat energy upon a part layer ofgreen material.

Optionally, the debinding applicator include may a debinding carriagethat main scans a part layer at a time (e.g., sprays and/or heats acrossthe width of a layer) to debind the debinder, and a portion of the fumeextractor is transported together with the debinding carriage to removedebound binder from a position continuously adjacent the debindingcarriage.

Further optionally, the debinding applicator may include a solvent bathinto which the part is immersed and removed before subsequent part layerdeposition by the print head.

Still further optionally, the print head may deposit part layers ofmodel material upon prior deposited part layers that have not beendebound by the debinding applicator as well as upon layers that havebeen debound by the debinding applicator.

According to another aspect of the embodiments of the present invention,a method of reducing distortion in an additively manufactured part mayinclude forming a shrinking or densification linking platform ofsuccessive layers of composite, the composite including a metalparticulate filler in a debindable matrix. The debindable matrix mayinclude different components so as to be a one or two stage binder.Shrinking or densification linking supports are formed of the samecomposite above the shrinking platform. A desired part of the samecomposite is formed upon the shrinking platform and shrinking supports,substantially horizontal portions (e.g., overhangs, bridges, largeradius arches) of the desired part being vertically supported by theshrinking platform (e.g., directly, via the shrinking supports, or via arelease layer). A sliding release layer may be formed below theshrinking platform of equal or larger surface area than a bottom of theshrinking platform (e.g., as shown in FIG. 4) that reduces lateralresistance between the shrinking platform and an underlying surface(e.g., such as a build platform or a tray for sintering). The matrix isdebound sufficient to form a shape-retaining brown part assembly (e.g.,including a sparse lattice of remaining binder to hold the shape)including the shrinking platform, shrinking supports, and desired part.The shape-retaining brown part assembly formed from the same compositeis heated to shrink all of the shrinking platform, the shrinkingsupports, and the desired part together at a same rate as neighboringmetal particles throughout the shape-retaining brown part assemblyundergo atomic diffusion. According, uniform shrinking and the slidingrelease layer reduce distortion.

An apparatus of similar advantage may include a print head that depositsthe shrinking platform, the shrinking supports, and the desired part, asecond printhead that forms the sliding release layer, a debinding washthat debinds the shape-retaining brown part assembly, and a sinteringoven to heat and shrink the shrinking platform, the shrinking supports,and the desired part together at a same rate. Optionally, an open cellstructure including interconnections among cell chambers is deposited inat least one of the shrinking platform, the shrinking supports, and thedesired part; and a fluid debinder is penetrated into the open cellstructure to debind the matrix from within the open cell structure.Additionally, or alternatively, the shrinking platform, shrinkingsupports, and desired part may be formed to substantially align acentroid of the combined shrinking platform and connected shrinkingsupports with the centroid of the part. Further additionally or in thealternative, the shrinking supports may be interconnected to a side ofthe desired part by forming separable attachment protrusions of the samecomposite between the shrinking supports and the side of the desiredpart. Still further additionally or in the alternative, a lateralsupport shell may be formed of the same composite following a lateralcontour of the desired part, and the lateral support shell may beconnected to the lateral contour of the desired part by formingseparable attachment protrusions of the same composite between thelateral support shell and the desired part.

Further optionally, soluble support structures of the debindable matrixmay be formed, without the metal particulate filler, that resistdownward forces during the forming of the desired part, and the matrixdebound sufficient to dissolve the soluble support structures beforeheating the shape-retaining brown part assembly. Alternatively, or inaddition, soluble support structures of a release composite may beformed, the release composite including a ceramic particulate filler andthe debindable matrix, the soluble support structures resisting downwardforces during the forming of the desired part. Before heating theshape-retaining brown part assembly, the matrix may be deboundsufficient to form a shape-retaining brown part assembly including theshrinking platform, shrinking supports, and desired part, and todissolve the matrix of the soluble support structures.

Additionally, or in the alternative, the underlying surface may includea portable build plate. In this case, the shrinking platform may beformed above the portable build plate, and the sliding release layerformed below the shrinking platform and above the portable build platewith a release composite including a ceramic particulate and thedebindable matrix. The shape-retaining brown part assembly may besintered during the heating. The build plate, sliding release layer, andshape-retaining brown part assembly may be kept together as a unitduring the debinding and during the sintering. After sintering, thebuild plate, sliding release layer, shrinking platform, and shrinkingsupports may be separated from the desired part.

Optionally, part release layers may be formed between the shrinkingsupports and the desired part with a release composite including aceramic particulate filler and the debindable matrix, and theshape-retaining brown part assembly sintered during the heating. Thepart release layers and shape-retaining brown part assembly may be kepttogether as a unit during the debinding and during the sintering. Aftersintering, separating the part release layers, shrinking platform, andshrinking supports may be separated from the desired part. In this case,an open cell structure including interconnections among cell chambers inthe shrinking supports may be deposited, and a fluid debinder may bepenetrated into the open cell structure to debind the matrix from withinthe open cell structure.

According to another aspect of the embodiments of the present invention,a method of reducing distortion in an additively manufactured partincludes depositing, in successive layers, a shrinking platform formedfrom a composite, the composite including a metal particulate filler ina debindable matrix, and depositing shrinking supports of the samecomposite and above the shrinking platform. An open cell structureincluding interconnections is deposited among cell chambers in theshrinking supports. From the same composite, a desired part is depositedupon the shrinking platform and shrinking supports. The shrinkingplatform, shrinking supports, and desired part are exposed to a fluiddebinder to form a shape-retaining brown part assembly. The fluiddebinder is penetrated into the open cell structure to debind the matrixfrom within the open cell structure. The shape-retaining brown partassembly is sintered to shrink at a rate common throughout theshape-retaining brown part assembly.

Optionally, a sliding release layer is deposited below the shrinkingplatform of equal or larger surface area than a bottom of the shrinkingplatform that reduces lateral resistance between the shrinking platformand an underlying surface. Additionally, or in the alternative, partrelease layers are deposited between the shrinking supports and thedesired part with a release composite including a ceramic particulatefiller and the debindable matrix, and the part release layers andshape-retaining brown part assembly are kept together as a unit duringthe exposing and during the sintering. After sintering, the part releaselayers, shrinking platform, and shrinking supports are separated fromthe desired part. Further optionally, as shown in, e.g., FIGS. 8-10,vertical gaps without release composite are formed between shrinkingsupports and the desired part where a vertical surface of a shrinkingsupport opposes an adjacent wall of the desired part.

Alternatively, or in addition, as shown in, e.g., FIGS. 8-10, a lateralsupport shell block is deposited having a large cell interior, havingcells with cell cavities wider than a thickest wall within the lateralsupport shell block, to assist in diffusing and penetrating debindingfluid into the support. Further alternatively, or in addition, theshrinking supports may be interconnected to a side of the desired partby forming separable attachment protrusions of the same compositebetween the shrinking supports and the side of the desired part.

Further optionally, as shown in, e.g., FIGS. 8-10, a lateral supportshell of the same composite as the shrinking supports may be depositedto follow a lateral contour of the desired part. In this case, thelateral support shell may be connected to the lateral contour of thedesired part by forming separable attachment protrusions of the samecomposite between the lateral support shell and the desired part.Alternatively, or in addition, at least one of the shrinking platform,the lateral support shell and the desired part may be deposited withinterconnections between internal chambers, and a fluid debinder may bepenetrated via the interconnections into the internal chambers to debindthe matrix from within the open cell structure. The shrinking platform,shrinking supports, and desired part may be deposited to substantiallyalign a centroid of the combined shrinking platform and connectedshrinking supports with the centroid of the part.

According to another aspect of the embodiments of the present invention,a method of reducing distortion in an additively manufactured partincludes depositing, in successive layers, a shrinking platform formedfrom a composite, the composite including a metal particulate filler ina debindable matrix. Shrinking supports of the same composite may bedeposited above the shrinking platform. As shown in, e.g., FIGS. 8-10,among the shrinking supports, parting lines as separation clearances maybe formed dividing the shrinking supports into fragments separable alongthe separation clearances. From the same composite, a desired part maybe shaped upon the shrinking platform and shrinking supports. The matrixmay be debound sufficient to form a shape-retaining brown part assemblyincluding the shrinking platform, shrinking support columns, and desiredpart. The shape-retaining brown part assembly may be sintered to shrinkat a rate uniform throughout the shape-retaining brown part assembly.The shrinking supports may be separated into fragments along theseparation clearances, and the fragments may be separated from thedesired part.

Optionally, one or more separation clearances are formed as verticalclearance separating neighboring support columns and extending forsubstantially an height of the neighboring support columns, and furthercomprising, and the neighboring support columns are separated from oneanother along the vertical clearances. Alternatively, or in addition,within a cavity of the desired part, interior shrinking supports areformed from the same composite. Among the interior shrinking supports,parting lines may be formed as separation clearances dividing theinterior shrinking supports into subsection fragments separable alongthe separation clearances. The subsection fragments may be separatedfrom one another along the separation clearances.

Alternatively, or in addition, the fragments are formed as blocksseparable from one another along a separation clearance contiguouswithin a plane intersecting the shrinking supports. A lateral supportshell of the same composite as the shrinking supports may be formed tofollow a lateral contour of the desired part. Optionally, the lateralsupport shell may be connected to the lateral contour of the desiredpart by forming separable attachment protrusions of the same compositebetween the lateral support shell and the desired part. Furtheroptionally, in the lateral support shell, parting lines may be formeddividing the lateral support shell into shell fragments separable alongthe parting lines. The matrix may be debound sufficient to form ashape-retaining brown part assembly including the shrinking platform,shrinking support columns, lateral support shell, and desired part. Thelateral support shell may be separated into the shell fragments alongthe parting lines. The shell fragments may be separated from the desiredpart.

Further optionally, at least one of the shrinking platform, theshrinking supports, and the desired part may be deposited withinterconnections between internal chambers, and a fluid debinderpenetrated via the interconnections into the internal chambers to debindthe matrix from within the open cell structure. Alternatively, or inaddition, soluble support structures of the debindable matrix withoutthe metal particulate filler may be formed that resist downward forcesduring the forming of the desired part, and the matrix deboundsufficient to dissolve the soluble support structures before sinteringthe shape-retaining brown part assembly.

Still further optionally, a sliding release layer may be formed belowthe shrinking platform of equal or larger surface area than a bottom ofthe shrinking platform that reduces lateral resistance between theshrinking platform and build plate, and the shrinking platform may beformed above the portable build plate. The sliding release layer may beformed below the shrinking platform and above the portable build platewith a release composite including a ceramic particulate and thedebindable matrix, the build plate, sliding release layers andshape-retaining brown part assembly may be kept together as a unitduring the debinding and during the sintering.

Further alternatively or in addition, part release layers may be formedbetween the shrinking supports and the desired part with a releasecomposite including a ceramic particulate filler and the debindablematrix, and the part release layers and shape-retaining brown partassembly may be kept together as a unit during the debinding and duringthe sintering. After sintering, the part release layers, shrinkingplatform, and shrinking supports may be separated from the desired part.

According to another aspect of the embodiments of the present invention,in a method for building a part with a deposition-based additivemanufacturing system, a polymer-including material is deposited along afirst contour tool path to form a perimeter path of a layer of the greenpart and to define an interior region within the perimeter path. In asecond direction retrograde the first direction, the material isdeposited based on a second contour tool path to form an adjacent pathin the interior region adjacent the perimeter path, the deposition ofthe adjacent path in the second direction stresses polymer chains in thematerial in a direction opposite to stresses in polymer chains in thematerial in the perimeter path, and reduces part twist caused byrelaxation of the polymer chains in the part.

Optionally, one of a start of deposition or a stop of deposition isadjusted to be located within the interior region of the layer. Furtheroptionally, the locations of the start point and the stop point definean arrangement selected from the group consisting of an open-squarearrangement, a closed-square arrangement, an overlapped closed-squarearrangement, an open-triangle arrangement, a closed-trianglearrangement, a converging-point arrangement, an overlapped-crossarrangement, a crimped-square arrangement, and combinations thereof.Alternatively, or in addition, a contour tool path between the startpoint and the stop point further defines a raster path that at leastpartially fills the interior region.

According to another aspect of the embodiments of the present invention,in a method for building a part with a deposition-based additivemanufacturing system having a deposition head and a controller, a firsttool path for a layer of the part is received by the controller, whereinthe received first tool path comprises a perimeter contour segment. Asecond tool path for a layer of the part is received by the controller,wherein the received second tool path comprises an interior regionsegment adjacent the perimeter contour segment. A deposition head ismoved in a pattern that follows the perimeter contour segment of thereceived first tool path to produce a perimeter path of a debindablecomposite including sinterable powder; and moving the deposition head ina pattern that follows the interior region segment of the receivedsecond tool path to produce an interior adjacent path of the debindablecomposite, wherein the perimeter path and the adjacent path aredeposited in directions so that directions of residual stress within abinder of the debindable composite are opposite in the perimeter pathand the adjacent path.

According to still another aspect of the embodiments of the presentinvention, in a method for building a part with a deposition-basedadditive manufacturing system, a digital solid model (e.g., 3D mesh or3D solid) of the part is received, and the digital solid model is slicedinto a plurality of layers. A perimeter contour tool path is generatedbased on a perimeter of a layer of the plurality of layers, wherein thegenerated perimeter contour tool path defines an interior region of thelayer. An interior adjacent path is generated based on the perimetercontour tool path within the interior region. A debindable composite isextruded including sinterable powder in a first direction based on theperimeter contour tool path to form a perimeter of the debindablecomposite for the layer. The debindable composite is extruded in asecond direction based on the perimeter contour tool path to form aninterior adjacent path of the debindable composite for the layer,wherein the deposition of the perimeter contour tool path and theinterior adjacent path are traced in retrograde directions to oneanother so that directions of residual stress within a binder of thedebindable composite are opposite in the perimeter contour tool path andthe interior adjacent path. Optionally, a start point of the perimetercontour tool path and a stop point of the perimeter contour tool pathare adjusted to locations within the interior region.

According to still another aspect of the embodiments of the presentinvention, in method for building a part with a deposition-basedadditive manufacturing system having a deposition head and a controller,a first tool path for a layer of the part is received by the controller,wherein the received first tool path comprises a contour segment. Asecond tool path for a layer of the part is received by the controller,and the received second tool path may overlap the first tool path overat least 90 percent of a continuous deposition length of the second toolpath. The deposition head is moved in a pattern that follows the firsttool path to produce a perimeter path of a debindable composite for thelayer. The deposition head is moved in a pattern that follows the secondtool path in a retrograde direction to the first tool path to produce astress-offsetting path adjacent the perimeter path of debindablecomposite, such that directions of residual stress within a binder ofthe debindable composite are opposite in the perimeter path and thestress-offsetting path. Optionally, the second tool path is continuouslyadjacent at least 90 percent of the first tool path within the samelayer, and comprises an interior region path. Further optionally, thesecond tool path is continuously adjacent over at least 90 percent ofthe first tool path within an adjacent layer, and comprises a perimeterpath of the adjacent layer.

According to yet another aspect of the embodiments of the presentinvention, in a method for building a part with a deposition-basedadditive manufacturing system having a deposition head and a controller,a tool path is generated with a computer. Instructions for the generatedtool path are transmitted to the controller, and a debindable compositeis deposited from the deposition head while moving the deposition headalong the generated tool path to form a perimeter path of a layer of thepart. The perimeter path may include a first contour road portion, and asecond contour road portion, each of the first contour road portion andthe second contour road portion crossing one another with an even numberof X-patterns, forming an even number of concealed seams for the layer.

According to yet another aspect of the embodiments of the presentinvention, in a method for building a part with a deposition-basedadditive manufacturing system having a deposition head and a controller,the deposition head is moved along a first tool path segment to form aperimeter road portion for a layer of the part, and is moved along adirection changing tool path segment. The deposition head may be movedalong a second tool path segment to form a stress-balancing road portionadjacent to the perimeter road portion. Optionally, the directionchanging tool path segment is a reflex angle continuation between thefirst tool path segment and the second tool path segment within the samelayer. Further optionally, a debindable composite including a binder anda sinterable powder is deposited in a first direction about a perimeter.An interior path is deposited along the perimeter in a directionretrograde the first direction. The deposition of the adjacent pathstresses long-chain molecules in the binder in a direction opposite tostresses in the perimeter path, and reduces part twist during sinteringcaused by relaxation of the long-chain molecules in the part.

According to yet another aspect of the embodiments of the presentinvention, in a method of depositing material for additivemanufacturing, a composite material is fed including a binder matrix anda sinterable powder. Successive layers of a wall of a part are depositedto form a first access channel extending from an exterior of the part toan interior of the part. Successive layers of honeycomb infill in theinterior of the part are deposited to form a distribution channelconnecting an interior volume of the honeycomb infill to the firstaccess channel. The binder matrix is debound (e.g., dissolved) byflowing a debinding fluid through the first access channel and thedistribution channel within the interior volume of the honeycomb infill.

Optionally, successive layers of the wall of the part are deposited toform a second access channel extending from the exterior of the part tothe interior of the part, and the binder matrix is debound by flowing adebinding fluid in through the first access channel, via thedistribution channel, and out through the second access channel. Furtheroptionally, the first access channel is connected to a pressurizedsupply of debinding fluid to force debinding fluid through the firstaccess channel, distribution channel, and second access channel.Alternatively, or in addition, successive layers of honeycomb infill aredeposited in the interior of the part to form a plurality ofdistribution channels connecting an interior volume of the honeycombinfill to the first access channel, at least some of the plurality ofdistribution channels being of different length from other of thedistribution channels.

According to another aspect of the embodiments of the present invention,in a method of depositing material for additive manufacturing, a metalmaterial including a binder matrix and sinterable powdered metal havingan average particle diameter lower than 8 micrometers are fed, the metalmaterial having a first sintering temperature. A ceramic material is fedincluding a same binder matrix and a sinterable powdered ceramic, theceramic material including a mixture of a first ceramic having a highersintering temperature than the metal material with a second ceramichaving a lower sintering temperature than the metal material, theceramic material substantially matching a shrinking behavior of themetal material and having a second sintering temperature substantiallyin a same range as the first sintering temperature. Layers of the metalmaterial are formed by deposition upon a prior deposition of layers ofthe metal material, and layers of the metal material are formed bydeposition upon prior deposition of layers of the ceramic material. Atleast a portion of the binder matrix is debound from each of the metalmaterial and ceramic material. A part so formed from the metal materialand ceramic material is heated to the first sintering temperature,thereby sintering the first material and the second material. Successivelayers of a wall of a part are deposited to form a first access channelextending from an exterior of the part to an interior of the part, aswell as to form a distribution channel connecting an interior volume ofthe honeycomb infill to the first access channel. A binder matrixretaining sinterable powder is debound by flowing a debinding fluidthrough the first access channel and the distribution channel within theinterior volume of the honeycomb infill.

According to a further aspect of the embodiments of the presentinvention, in method of depositing material to form a sinterable brownpart by additive manufacturing, a first filament feeding along amaterial feed path, the first filament including a binder matrix andsinterable spherized and/or powdered first material having a firstsintering temperature. A green layer of first material is formed bydeposition upon a brown layer of first material. At least a portion ofthe binder matrix is debound from each green layer of first material todebind each green layer into a corresponding brown layer. Following theformation of substantially all brown layers of the part, the part may besintered at the first sintering temperature.

In an alternative, or in addition, in a method of depositing material toform a sinterable brown part by additive manufacturing, a first filamentis fed including a binder matrix and sinterable spherized and/orpowdered first material having a first sintering temperature. A secondfilament is fed including a second material having a second sinteringtemperature more than 300 degrees C. higher than the first sinteringtemperature. Layers of second material are formed by deposition upon abuild plate or prior deposition of first or second material. Greenlayers of first material are formed by deposition upon prior depositionof a brown layer or second material, and at least a portion of thebinder matrix from each green layer of first material is debound, todebind each green layer into a corresponding brown layer. Following theformation of substantially all brown layers of the part, the part may besintered at the first sintering temperature but below the secondsintering temperature, thereby sintering the first material withoutsintering the second material.

According to another aspect of the embodiments of the present invention,in a method of sintering a brown part article formed from a powderedsinterable material, a brown part integrally formed from a first powderhaving a first sintering temperature in a powder bed is placed within acrucible, the powder bed including a second powder having a secondsintering temperature more than 300 degrees C. higher than the firstsintering temperature. The second powder is agitated to fill internalcavities of the brown part. A weight of an unsupported portion of thebrown part is continually resisted with the second powder. The brownpart is sintered at the first temperature without sintering the secondpowder to form a sintered part. The sintered part is removed from thepowder bed.

Optionally, the agitating includes fluidizing the second powder byflowing a pressurized gas into the bottom of the crucible.Alternatively, or in addition, the weight of an unsupported portion ofthe brown part is continually resisted with the second powder, at leastin part by maintaining a buoyant force having an upward component in thefluidized second powder.

According to another aspect of the embodiments of the present invention,in a method of fabricating a 3D printed from a powdered sinterablematerial, a first filament is fed including a binder matrix andsinterable spherized and/or powdered first material having a firstsintering temperature. A second filament is fed including a secondmaterial having a second sintering temperature more than 300 degrees C.higher than the first sintering temperature. Layers of second materialare formed by deposition upon a build plate or a prior deposition offirst or second material, and green layers of first material are formedby deposition upon prior deposition of a brown layer or second material.At least a portion of the binder matrix from each green layer of firstmaterial is debound, to debind each green layer into a correspondingbrown layer. The part is placed integrally in a powder bed within acrucible, the powder bed including a third powder having a thirdsintering temperature more than 300 degrees C. higher than the firstsintering temperature. The third powder is agitated to fill internalcavities among the brown layers, and a weight of an unsupported portionof the brown layers is continually resisted with the third powder. Thepart is sintered at the first temperature without sintering the thirdpowder to form a sintered part, and the sintered part is removed fromthe powder bed.

According to another aspect of the embodiments of the present invention,in a method for additive manufacturing, a material is suppliedcontaining a removable binder and greater than 50% volume fraction of apowdered metal having a melting point greater than 1200 degrees C., inwhich more than 50 percent of powder particles of the powdered metalhave a diameter less than 10 microns. The material is additivelydepositing in successive layers to form a green body, and the binder isthen removed to form a brown body. The brown part or body is loaded intoa fused tube formed from a material having an operating temperature lessthan substantially 1200 degrees C., a thermal expansion coefficientlower than 1×10-6/° C. and a microwave field penetration depth of 10 mor higher. The fused tube is sealed and internal air is replaced with asintering atmosphere. Microwave energy is applied outside the sealedfused tube to the brown part. The brown part is sintered a temperaturelower than 1200 degrees C.

According to a further aspect of the embodiments of the presentinvention, in a method for additive manufacturing, a material issupplied containing a removable binder and greater than 50% volume of apowdered metal having a melting point greater than 1200 degrees C., inwhich more than 50 percent of the powder particles have a diameter lessthan 10 microns. The material is additively deposited with a nozzlehaving an internal diameter smaller than 300 microns. The binder isremoved to form a brown body or part. The brown part or body is loadedinto a fused tube formed from a material having a thermal expansioncoefficient lower than 1×10-6/° C. The fused tube is sealed, andinternal air replaced with a sintering atmosphere. Radiant energy isapplied from outside the sealed fused tube to the brown part. The brownpart or body is sintered at a temperature higher than 500 degrees C. butless than 1200 degrees C.

According to a further aspect of the embodiments of the presentinvention, in a method for additive manufacturing, a first brown partmay be supplied formed from a first debound material including a firstpowdered metal, in which more than 50 percent of powder particles of thefirst powdered metal have a diameter less than 10 microns. A secondbrown part may be supplied formed from a second debound materialincluding a second powdered metal, in which more than 50 percent ofpowder particles of the second powdered metal have a diameter less than10 microns. In a first mode, the first brown part may be loaded into afused tube formed from a material having a thermal expansion coefficientlower than 1×10-6/° C., and a temperature inside the fused tube may beramped at greater than 10 degrees C. per minute but less than 40 Cdegrees C. per minute to a first sintering temperature higher than 500degrees C. and less than 700 degrees C. In a second mode, the secondbrown part may be loaded into the same fused tube, and a temperatureinside the fused tube may be ramped at greater than 10 degrees C. perminute but less than 40 degrees C. per minute to a second sinteringtempering temperature higher than 1000 degrees C. but less than 1200degrees C.

Optionally, in the first mode, a first sintering atmosphere isintroduced into the fused tube including inert Nitrogen being 99.999% orhigher free of Oxygen. Further optionally, in the second mode, a secondsintering atmosphere comprising at least 2%-5% (e.g., 3%) Hydrogen maybe introduced into the fused tube. Optionally, the fused tube is formedfrom a fused silica having a microwave field penetration depth of 10 mor higher, and microwave energy is applied to the first and/or secondmaterial brown parts within the fused tube, raising the temperature ofsame. Microwave energy may alternatively, or in addition applied to, toraising the temperature of, susceptor material elements placed outsidethe fused tube and outside any sintering atmosphere within the fusedtube.

In these aspects, optionally, the material is additively deposited at alayer height substantially ⅔ or more of the nozzle width. Optionally, amaterial is supplied in which more than 90 percent of powder particlesof the powdered metal have a diameter less than 8 microns. Furtheroptionally, microwave energy is applied from outside the sealed fusedtube to susceptor material members arranged outside the sealed fusedtube. Microwave energy may be the radiant energy applied from outsidethe sealed fused tube to the brown part. Susceptor material membersarranged outside the sealed fused tube may be resistively heated.Optionally, a temperature inside the fused tube may be ramped at greaterthan 10 degrees C. per minute but less than 40 degrees C. per minute.The material of the fused tube may be amorphous fused silica, and thesintering atmosphere may comprise at least 2% Hydrogen and no more than5% Hydrogen (e.g., 3% Hydrogen). The powdered metal may be a stainlesssteel or a tool steel. The susceptor material may be one of SiC orMoSi2.

According to an additional aspect of the embodiments of the presentinvention, a multipurpose sintering furnace, includes a fused tubeformed from a fused silica having a thermal expansion coefficient lowerthan 1×10-6/° C., and a seal that seals the fused tube versus ambientatmosphere. An internal atmosphere regulator is operatively connected toan interior of the fused tube to apply vacuum to remove gases within thefused tube and to introduce a plurality of sintering atmospheres intothe fused tube, and heating elements are placed outside the fused tubeand outside any sintering atmosphere within the fused tube. A controlleris operatively connected to the heating elements and the internalatmosphere regulator, the controller in a first mode sintering firstmaterial brown parts within a first sintering atmosphere at firstsintering temperature higher than 500 degrees C. and less than 700degrees C., and in a second mode sintering second material brown partswithin a second sintering atmosphere at a second sintering temperaturehigher than 1000 degrees C. but less than 1200 degrees C.

Optionally, the internal atmosphere regulator is operatively connectedto an interior of the fused tube to introduce a first sinteringatmosphere comprising inert Nitrogen being 99.999% or higher free ofOxygen. Further optionally, the controller in the first mode sintersbrown parts primarily formed with Aluminum powder in which more than 50percent of powder particles have a diameter less than 10 microns, withinthe first sintering atmosphere comprising inert Nitrogen being 99.999%or higher free of Oxygen, at the first sintering temperature higher than500 degrees C. and less than 700 degrees C. Alternatively, or inaddition, the controller in the second mode sinters brown partsprimarily formed with Steel powder in which more than 50 percent ofpowder particles have a diameter less than 10 microns, within the secondsintering atmosphere comprising at least 3% Hydrogen, at the secondsintering temperature higher than 1000 degrees C. and less than 1200degrees C.

The controller may ramp a temperature inside the fused tube at greaterthan 10 degrees C. per minute but less than 40 degrees C. per minute.The internal atmosphere regulator may be operatively connected to aninterior of the fused tube to introduce a second sintering atmospherecomprising at least 3% Hydrogen. The controller may ramp a temperatureinside the fused tube at greater than 10 degrees C. per minute but lessthan 40 degrees C. per minute. The fused silica tube may be formed froma fused silica having a thermal expansion coefficient lower than1×10-6/° C. and a microwave field penetration depth of 10 m or higher,and wherein the heating elements further comprise a microwave generatorthat applies energy to, and raises the temperature of, the first and/orsecond material brown parts within the fused tube. Susceptor materialheating elements may be placed outside the fused tube and outside anysintering atmosphere within the fused tube, wherein the microwavegenerator applies energy to, and raises the temperature of, one or bothof (i) the first and/or second material brown parts within the fusedtube and/or (ii) the susceptor material heating elements. The heatingelements further comprise susceptor material heating elements placedoutside the fused tube and outside any sintering atmosphere within thefused tube. A small powder particle size (e.g., 90 percent of particlessmaller than 8 microns) of metal powder embedded in additively depositedmaterial may lower a sintering temperature of stainless steels to belowthe 1200 degree C. operating temperature ceiling of a fused silica tubefurnace, permitting the same silica fused tube furnace to be used forsintering both aluminum and stainless steel (with appropriateatmospheres), as well as the use of microwave heating, resistantheating, or passive or active susceptor heating to sinter bothmaterials.

According to another aspect of the embodiments of the present invention,in a composite material including >50% metal or ceramic spheres, andoptionally with a two stage binder, a spool of filament material iswound and unwound at a temperature higher than room temperature but lessthan a glass transition temperature of a binder material, e.g., 50-55degrees Celsius. It may be transported in at room temperature. Upperspools in a model material chamber may include the model material andthe release material. The spools may be kept in a joint heated chamberwhich keeps the spools at the 50-55 degrees Celsius contemplated by thisexample. A build plate may be heated by a build plate heater to similaror higher temperature (e.g., 50-120 degrees C.) during printing. Theheating of the build plate may help maintains the temperature within theprinting compartment at a level above room temperature.

Optionally, each spool of material may be kept in its own independentchamber. A heater for maintaining the spool temperature may be passive,e.g., radiant and convection heater, or include a blower. Heated air maybe driven through Bowden tubes or other transport tubes through whichthe filament material is driven. The spools may be vertically arrangedon a horizontal axle, and the filament dropped substantially directlydown to the moving printing heads so as to have a large bend radius inall bends of the filament. The material may be maintained with no bendmore of smaller than a 10 cm bend radius, and/or no bend radiussubstantially smaller than that of the spool radius).

According to another aspect of the embodiments of the present invention,in a method for 3D printing green parts, a binder is jetted ontosuccessive layers of powder feedstock to form a 2D layer shape of boundpowder per layer. A 3D shape is additively deposited (e.g., built up) ofa desired 3D green part from interconnected 2D layer shapes of the boundpowder. A 3D shape of sintering supports is additively deposited (e.g.,built up) from interconnected 2D layer shapes of the bound powder, and a3D shape of a shrinking platform is additively deposited (e.g., builtup) from interconnected 2D layer shapes of the bound powder. A releasematerial is additively deposited (e.g., built up) upon shapes of boundpowder to form 2D layer shapes of release material, and a 3D shape ofrelease surfaces additively deposited (e.g., built up) frominterconnected 2D layer shapes of the release material. A placeholdermaterial is additively deposited (e.g., built up) upon shapes of boundpowder to form 2D layer shapes of placeholder material, and a 3D shapeof placeholder volumes is additively deposited (e.g., built up) frominterconnected 2D layer shapes of the placeholder material. The boundpowder, release material, and placeholder material are debound to form agreen part assembly including the desired 3D green part, the sinteringsupports, the release surfaces, and internal cavities corresponding tothe 3D shapes of the placeholder material before debinding.

According to this aspect, for 3D printing green parts to be debound andsintered, a binder may be jetted into successive layers of sinterablepowder feedstock to build up a 3D shape of a desired 3D green part,associated sintering supports, and an associated shrinking platform. Arelease material may be deposited to intervene between the 3D greenparts and the sintering supports. A placeholder material may bedeposited upon bound powder to form 2D layer shapes of placeholdermaterial, and the sinterable powder feedstock refilled and leveled aboutthe placeholder material. Upon debinding, internal cavitiescorresponding to the 3D shapes of the placeholder material are formed.

According to another aspect of the embodiments of the present invention,an apparatus for additive manufacturing by depositing sinterablepowdered metal in a soluble binder include a nozzle assembly, includinga nozzle body within which is formed a first central cylindrical cavityof substantially constant diameter and a nozzle outlet connected to thecylindrical cavity, the nozzle outlet being of 0.1-0.4 mm diameter. Aheat break member abuts the nozzle assembly, the heat break memberincluding a heat break body having a narrowed waist portion, a secondcentral cylindrical cavity of substantially constant diameter beingformed through the heat break body and narrowed waist portion. A meltchamber is formed shared by the first and second central cylindricalcavity, the melt chamber being of 15-25 mm{circumflex over ( )}3 volumeand 1 mm or less in diameter.

According to another aspect of the embodiments of the present invention,a 3D printer may deposit, from the powdered metal (or ceramic) andbinder composites discussed herein, a densification linking platformthat is equal to or larger than a lateral or horizontal extent of adesired part, e.g., a minimum size that corresponds to the envelope ofthe part, at least partially separated from the part by a ceramicrelease layer. The thickness of the densification linking platformshould be at least ½ mm-10 mm thick such that the forces developedduring the shrinking process from atomic diffusion in the raftsubstantially counteract the friction force between the brown bodyassembly and a plate or carrier upon which sintering is performed. Thedesired part may be optionally tacked to the densification linkingplatform with small-cross sectional area (e.g., less than ⅓ mm diameter)connections of the metal composite material that penetrate the ceramicrelease layer vertically in order to ensure that the part shrinks in thesame geometric manner as the densification linking platform that it isresting on. The densification linking platform is optionally formedhaving a cross-sectional area in the shape of a convex shape (a polygonor curved shape without concavities), and/or in a symmetric shape havinga centroid aligned with that of the part above. The densificationlinking platform tends to densify and shrink in a regular or predictablemanner due to its simple geometry, and if as the desired part isconnected to the raft it decreases geometry specific part distortionthat arises from the friction forces between the desired part and thedensification linking platform, especially in the case of asymmetricparts, parts with high aspect ratio cross sections, and parts withvariable thicknesses. The number and placement of tack points betweenthe part and the raft may be selected such that the raft can be suitablyremoved after the sintering process. Optionally, vertical walls outsidethe perimeter of the part that are solidly attached to the densificationlinking may extend at least partially up the sides of the desired partto further reduce distortion. These vertical supports may also beseparated from the desired by the ceramic release layer.

It is expressly contemplated that the foregoing examples of aspects ofembodiments of the present invention, when combined individually or inmultiple combinations, form additional examples of aspects ofembodiments of the present invention.

At least one aspect of the invention is directed to a method for 3Dprinting green parts, comprising jetting a binder onto successive layersof powder feedstock in a powder bed to form a 2D layer shape of boundpowder per layer, building up a 3D shape of a first desired 3D greenpart from interconnected 2D layer shapes of the bound powder, buildingup a 3D shape of sintering supports from interconnected 2D layer shapesof the bound powder, building up a 3D shape of a shrinking platform frominterconnected 2D layer shapes of the bound powder, and forming a greenpart assembly including the first desired 3D green part, the sinteringsupports, and the shrinking platform.

According to one embodiment, the method further comprises applying arelease material upon shapes of bound powder to form a 2D layer shape ofrelease material. In one embodiment, the method further comprisesbuilding up a 3D shape of a release surface from interconnected 2D layershapes of the release material, wherein forming the green part assemblyincludes forming the green part assembly including the release surface.In another embodiment, applying the release material includes applyingthe release material to form a complementary 2D layer shape interveningbetween a sintering support and the first desired 3D green part.

According to another embodiment, the method further comprises applying aplaceholder material upon shapes of bound powder to form a 2D layershape of placeholder material. In one embodiment, the method furthercomprises building up a 3D shape of placeholder volumes frominterconnected 2D layer shapes of the placeholder material, whereinforming the green part assembly includes forming the green part assemblyincluding an internal cavity corresponding to the 3D shape of theplaceholder material. In another embodiment, applying the placeholdermaterial includes applying the placeholder material to form acomplementary 2D layer shape of desired free space within the desiredpart or the sintering supports. In one embodiment, applying theplaceholder material includes applying the placeholder material to forma 2D layer shape of a shell, the shell capturing unbound powderfeedstock within. In another embodiment, jetting the binder includesjetting the binder onto the powder feedstock within the shell to form areinforcement shape within the shell.

According to one embodiment, applying the placeholder material includesapplying the placeholder material to form a complementary 2D layer shapeof adhesive between the shrinking platform and an underlying buildplatform. In one embodiment, applying the placeholder material includesapplying the placeholder material to form a complementary 2D layer shapeof adhesive on the first desired 3D green part. In another embodiment,the method further comprises building up a 3D shape of a second desired3D green part from interconnected 2D layer shapes of the bound powder,the second desired 3D green part stacked on the complementary 2D layershape of adhesive on the first desired 3D green part.

According to another embodiment, jetting includes jetting the binderonto successive layers of one of sinterable powder feedstock and ceramicpowder feedstock to form the 2D layer shape of bound powder per layer.In one embodiment, the method further comprises refilling the powder bedwith new or recycled powder feedstock with each successive layer. Inanother embodiment, the method further comprises leveling the refilledpowder feedstock with a powder leveling mechanism for each successivelayer. In one embodiment, the method further comprises shaping one ofthe 2D layer shapes of bound powder with a surface finishing mechanismprior to refilling the powder bed.

According to one embodiment, jetting includes adjusting an amount ofbinder jetted onto a layer of the powder feedstock based on whether anouter portion of the 2D layer shape or an inner portion of the 2D layershape is being formed. In one embodiment, the method further comprisesremoving the green part assembly from the powder feedstock in the powderbed, and removing unbound power from the green part assembly. In anotherembodiment, removing the unbound powder includes removing the unboundpower from surroundings of the first desired 3D green part and thesintering supports via outlets formed in the bound powder.

Another aspect of the invention is directed to a method for 3D printinggreen parts, comprising jetting a binder onto successive layers ofpowder feedstock in a powder bed to form a 2D layer shape of boundpowder per layer, building up a 3D shape of a desired 3D green part frominterconnected 2D layer shapes of the bound powder, applying aplaceholder material upon shapes of bound powder to form 2D layer shapesof placeholder material, building up a 3D shape of placeholder volumesfrom interconnected 2D layer shapes of the placeholder material, andforming a green part assembly including the desired 3D green part and acavity corresponding to the 3D shape of the placeholder material.

According to one embodiment, applying the placeholder material includesapplying the placeholder material to form 2D layer shapes of a shell,the shell surrounding the cavity. In one embodiment, forming the 2Dlayer shapes of the shell includes capturing unbound powder feedstockwithin the shell. In another embodiment, jetting the binder includesjetting the binder onto the powder feedstock within the shell to form areinforcement shape within the shell. In one embodiment, the methodfurther comprises removing the unbound power from surroundings of thedesired 3D green part via outlets formed in the bound powder. In anotherembodiment, applying the placeholder material includes applying theplaceholder material to form a 2D layer shape of a mold defining anouter skin of the desired 3D part.

According to another embodiment, applying the placeholder materialincludes applying the placeholder material to form a complementary 2Dlayer shape of adhesive on an underlying build platform. In oneembodiment, applying the placeholder material includes applying theplaceholder material to form a complementary 2D layer shape of adhesiveon the desired 3D green part. In another embodiment, the method furthercomprises removing the placeholder material from the green part assemblyprior to sintering the green part assembly. In one embodiment, themethod further comprises sintering the green part assembly including theplaceholder material.

At least one aspect of the invention is directed to a method for 3Dprinting green parts, comprising jetting a binder onto successive layersof powder feedstock to form a 2D layer shape of bound powder per layer,building up a 3D shape of a desired 3D green part from interconnected 2Dlayer shapes of the bound powder, building up a 3D shape of sinteringsupports from interconnected 2D layer shapes of the bound powder,building up a 3D shape of a shrinking platform from interconnected 2Dlayer shapes of the bound powder, applying a release material uponshapes of bound powder to form 2D layer shapes of release material,building up a 3D shape of release surfaces from interconnected 2D layershapes of the release material, applying a placeholder material uponshapes of bound powder to form 2D layer shapes of placeholder material,building up a 3D shape of placeholder volumes from interconnected 2Dlayer shapes of the placeholder material, and forming a green partassembly including the desired 3D green part, the sintering supports,the release surfaces, and internal cavities corresponding to the 3Dshapes of the placeholder material before debinding.

In 3D printing of metal parts, support structures may be used to bothenable the printing of the part, and to support the part duringsintering. Sintering or sinterable ceramic release layers (includingseparation tacks—columns or bridges—i.e., connections between a desiredpart and a sintering support which partially or entirely sinter into abrittle, but sintered tack) may allow parts to be easily removed fromtheir support structures after sintering of both the model material andthe separation tack. Although all of the ceramic separation tacks may besintered to brittle states or form a brittle layer, these layers mayalso include some loose powder, in contrast to release layers madeentirely of loose powder.

Sintering occurs in stages and is driven by the high surface energyinherent to a powder. The initial stage of sintering corresponds to neckgrowth at the contact points of the powders. During this initialsintering stage there is little to no dimensional change since necks areformed by surface and lattice diffusion. There is at most 3% linearshrinkage observed. A number of factors can affect the rate andtemperature at which the particles start necking or sintering such asparticle size, shape and chemistry. Smaller powders will sinter at alower temperature as it has greater surface energy. [Reference:Thermodynamics of sintering, R. M German chapter 1 of Sintering ofAdvanced materials Whiteheat publishing limited 2010] We considerparticles that have neck growth to have begun sintering and may refer tothem as tacks or flakes. Particles that have not been heatedsufficiently to start necking or sintering is a considered to still be apowder.

Release layers, including sintering ceramic separation tacks (optionallyformed as a disk, spot, dash, ridge, line, zig-zag, or the like), thatdo not wholly become loose powder in a sintering process reduce thehazards of powder handling and cleanup required when separating a partfrom the support structure. In one embodiment, stainless steel sinteredbetween 1150-1250 C achieves 97-98% density, and shrinks to a near netshape. An exemplary sintering ceramic release layer may include aluminapowder (before sintering) of 0.04-4 um diameter (spherical ornear-spherical particles) alumina (preferably 1-2 um).

In another embodiment, the particles within the release layer mayincorporate more than one particle feedstock material. For example, abimodal particle size distribution may be used by mixing small and largeparticles such as 80 nm alumina particles with 5 um alumina particles inorder to achieve a sintering separation layer with tunable mechanicalproperties. This may also be done to save cost. Alternatively, particleswith different chemical compositions may be mixed to further modify themechanical properties. One example may be 40 nm zirconia powder mixedwith 5 um alumina. Mechanical properties that may be tuned in thismanner include but are not limited to mechanical strength and shrinkagefor a given sintering temperature profile.

A ceramic layer that does not reduce to powder and instead is sinteredmay fragment, e.g., breaking into flakes when removing the part from thesupport. While a ceramic material has advantages, the material of thesintering support tack be any non reactive material such as aluminumoxide, a stabilized zirconium oxide, silicon oxide or a refractorymetal. One example separation material includes 5-40% by volume aluminumoxide (Al2O3) powder bound in a polymer mixture. The powder may be 99.2%alpha phase alumina and substantially spherical. The average particlesize may be 0.04-5 microns, e.g., 2 microns.

One of the binder components may be soluble in Opteon Sion(trans-Dichloroethylene mixed with proprietary fluorocarbon). Anoptional secondary binder component may not soluble in Opteon Sion, andmay thermally decompose cleanly around ˜420 C degrees (e.g., 350-470degrees C.). The binder system may substantially dissolve in the stepdesigned to debind the metal part, or may not dissolve depending on theformulation.

Another embodiment disclosed herein incorporates a multiple stepsintering process. The first sintering step may be performed at a first,lower temperature sintering temperature or ramp (e.g., 1000-1150 C)achieving a metal part density of at least 95% of theoretical, whilekeeping the ceramic release layer material, including support tacks, apowder, allowing for the compacting or densifying metal to move andsometimes or in some locations compact the ceramic (powder) withoutcausing excess distortion of the metal during shrinkage. After themajority of the shrinking is complete, the combined part and support andsintering ceramic support layer, tack, or tack layer may then be broughtup to a second, higher temperature sintering step (e.g. between 1150C-1400 C) sintering the ceramic and sometimes further densifying themetal.

Another embodiment disclosed herein incorporates a sintering ceramicsupport structure with some amount of metal scaffolding inside such thatthe both components of the support structure sinter and shrink with themetal part. In this embodiment it is advantageous for the sinteringceramic support structure to shrink at the same rate or more than themetal at the desired sintering temperature. In this manner the sinteringceramic support structure provides printing supports while printing thegreen body, while the metal scaffolding provides support during thesintering process and shrinks at the same rate as the part. The supportstructure can be removed after sintering with the application of amechanical energy to separate the solid sections. Another embodimentinvolves using a sintering ceramic support material that does notmaintain it's mechanical shape during the sintering process. A sinteringceramic support material comprising less than 25% solids by volume maycollapse to form a powder during the mid-stages of the sinteringprocess, and then sinter into an easily removable flake or otherwisepartially sintered form during the final stages of the sinteringprocess. The metal scaffold provides the structural and shrinkingsupport while the sintering ceramic material that is trapped between themetal scaffold and the part prevents excessive tacking of the part tothe support structure.

Another embodiment disclosed herein incorporates the intentionaladdition of physical connections or tacking between the part and thecommon-material sintering supports, and/or among or through thesintering ceramic support tack, tack layer, or layer. In many cases, andespecially in circumstances where the geometry of the part and sinteringsupport structure lead to a shear force between the two due to gravity,it may be advantageous for the part to remain physically connectedthrough these other tacking points to the support structure throughoutthe debinding and sintering process. As explained, some tacks aremetal-metal (the part/support tacks) and some tacks may bemetal-ceramic-metal (the part/sintering ceramic tack/support tacks).

Tacking metal to support across the region or layer of sintering supporttacks may allow the part and the support structure to overlap andconnect through the sintering ceramic layer. For example smallconnections of metal that pass through the sintering separation layer(e.g., sintering ceramic tacks, tack layer, or layer. optionallyincluding some powder) to physically connect the part to the supportstructure. These connections can be formed by spacing individual linesof extruded sintering ceramic release material far enough apart suchthat portions of the extruded lines do not touch (there are gaps,between the beads of extruded ceramic material). In a flat plane, thisdeposition can look like a continuous ceramic path where the underlyingsupport structure can be seen through the extruded ceramic. The materialused to form the part (optionally the same material as the supportstructure) can then be extruded on top of the sinterable release layer(including support tack material) in a manner that causes the partmaterial to flow between the lines of the sparse separation andoccasionally form bonds or tacks between the part and support structure.This stochastic process may lead to a part/support superstructure ormingling that remains intact throughout the debinding and sinteringprocess, but can be separated with the addition of mechanical energy.The ceramic path may be discontinuous, partial, and in some places, theextruded ceramic beads may touch. The path may enable some overlapbetween the part and support structure through the ceramic separation orsinterable ceramic layer (including tack layer). In one embodiment, arepresentative general composition for a 3D printing feedstock includinga separation powder and a binder includes a ceramic powder (adistribution of particles with mean size of 1 nm-5 um, preferably 20nm-2 um, more preferably 1 um), with one or more polymer or smallmolecule binders, and optionally a compatibilizer. In anotherembodiment, a representative general composition for a 3D printingfeedstock including a separation powder and a binder includes a ceramicpowder (a distribution of particles with mean size of 25 nm-50 um,preferably 3 nm-10 um, more preferably 5 um), with one or more polymeror small molecule binders, and optionally a compatibilizer.

The binder can include a component that thermally decomposes withminimal residue and has a component that can be removed with a solvent.Example polymer systems include polymers in the polyolefin family aswell as hydrocarbon based waxes. More preferably the polymer componentincludes a mixture of polypropylene and poly(propylene-co-ethylene). Oneexample separation material is composed of 25% by volume aluminum oxide(Al2O3) powder bound in a polymer mixture. The powder may be 99.2% alphaphase alumina and substantially spherical. In one embodiment, theaverage particle size may be 0.040-4 microns. In another embodiment, theaverage particle size may be 1-10 microns, e.g. 5 microns. A polymercomponent may be about ˜40% by weight, may not be soluble in Opteon Sion(trans-Dichloroethylene mixed with proprietary fluorocarbon) and maythermally decompose cleanly around ˜420 C degrees.

A useful alternative may include a component that allows for debindingthrough the layer (e.g., wax paired with Opteon Sion solvent debind, PEOpaired with water debind, Ethocel paired with thermal debind, etc).There are alternative material pairs such as titanium and its alloyswith stabilized zirconia powder (e.g. ti64 with YSZ or Calciumstabilized zirconia). At lower sintering temperature one may use otherceramics such as silica. An alternative to ceramics is using arefractory metal powder. Other additions that could be useful includereducing agents such as titanium hydride, plasticizers or extrusionmodifiers to change the rheological properties. Another alternative tospherical powders is to use hollow or nonspherical powders. An upperlimit of utility may be a sintering loading of powder ˜60% volume ofalumina with the same polymer binder/matrix used for a 17-4 steel powderof model material. A 60% by volume loading of ceramic powder, however,may cause sintering 17-4 steel powder, i.e., a sintering metal part orsupport, to warp during sintering as excessive ceramic powder is trappedbetween the support and part as the model material steel or other metalshrinks. Powder loading may be reduced by mixing in one or more binders,for example polypropylene and or paraffin wax with the feedstock duringextrusion to obtain powder loading of, e.g., 40%, 30%, 25%, 10% byvolume. The loading cannot be so low that there is insufficient materialto prevent a permanent connection between the support metal and thepart.

A wax component may be useful but is more difficult to extrude.Empirically, 25% by volume prints well, and a lower limit, e.g., 20%,15%, 10%, or 5% may be reached at which the remaining ceramic powderafter sintering no longer serves to help separate sintering supportsfrom a desired part.

A 25% loading ceramic material may be blended with LDPE (low densitypolyethylene), which may have a low melting point and may notnecessarily remain solid on a hot part after extruding. A 25% loading ofceramic material performs better with PP (polypropylene).

In some cases, the ceramic powder used in the separation material andseparation layer should not be reactive with the part, model, or metalmaterial and should not sinter together at the part, model, or metalsintering temperature. Alumina (Al2O3) powder is not reactive with steel(of various grades) so Alumina is an appropriate separation layermaterial. An advantage of the alumina separation material composition isthat the polymer component breaks down cleanly at the same temperatureas that of the polymer binding metal material, so the debinding andsintering routine and hardware (filter, gas used, wax trap etc) mayremain the same for parts with and without supports and/or separationlayers. Lower powder loading (e.g., 35-15% by volume) may mean afilament is more flexible at room temperature so it doesn't break in theprinter or in general handling of it.

In some cases, after sintering, the ceramic powder remains. In somecases this powder needs to be handled with powder-oriented safetyprocedures. Some procedures may be avoided by using smaller powderand/or sintering hotter to get partial sintering of the ceramicseparation material.

In some case, the wash time is increased for a part with a sinteringceramic separation layer since the solvent cannot debind through thesintering ceramic separation layer. This may be overcome by adding acomponent such as a wax that does debind in a solvent. Highly loadedceramic powder (e.g., >40% by volume) separation material may bedifficult to extrude (more viscous), may jam nozzles more easily, andmay string more while printing—these problems may be reduced by reducingthe powder content to 15-35%, e.g., 25% by volume.

The sinterable ceramic separation material may be extruded out of anozzle on the printhead just like the metal powder model material. Theprinter is substantially the same as described herein. However, thenozzle outlet on the separation material may be larger than that of themodel material because the separation material does not form part of thesurface of the part (i.e., does not contribute to resolution of thepart). Accordingly, the separation material may be printed via a largernozzle, e.g. 25%-300% larger, e.g., in some cases 25%-150% largerdiameter. In one example, the ceramic nozzle has a larger opening of 400um versus a 250 um nozzle opening for model material.

The separation material may be printed at a lateral or translation speedslower than that of the model material, e.g., 10-75% of the speed, e.g.,in some cases ¼ of the speed. In one example, the separation material isprinted at substantially ¼ the lateral speed of the metal MIM materialfor the part, e.g., a MIM printhead speed 1000 mm/min, with an extruderspeed 80 mm/min, matched to a sinterable ceramic separation materialprinthead speed of 250 mm/min, extruder speed 20 mm/min. Printingseparation material above these speeds tends to jam the ceramic nozzle.

The viscosity range of the separation material loaded with a loweramount of powder, e.g., 15-35% by volume of powder, such as 25% powder,may be in the range of 15-250 Pa s (at shear rate of 100/s) to 150-3000Pa s (for shear rate of 1000/s). One exemplary material loaded with alower amount of powder, e.g., 15-35% by volume of powder, such as 25%powder, may have a viscosity of 50 Pa s (at shear rate of 100/s) and 200Pa s (for shear rate of 1000/s).

With a sinterable ceramic separation material loaded with a lower amountof powder, e.g., 15-35% by volume of powder, such as 25% powder, afterthe nozzle lays down a bead of ceramic material and the filament isretracted to laterally transit the release material printhead to anotherstarting location, the viscosity of the ceramic material may lead tostringing instead of a clean termination of the part. In order to avoidstringing, each separation material extrusion or print cycle may beterminated by a wiping process, e.g., at the end of every ceramicextrusion to 1) retract, 2) move up in Z by 0.5 layer height, 3) retraceoriginal path up to 20 mm, 4) move up in Z further and then travel away.This behavior effectively “wipes” the trailing thread of ceramic on thebead that was just laid down.

The ceramic separation material loaded with a lower amount of powder,e.g., 15-35% by volume of powder, such as 25% powder, held hot in theprinting nozzle for extended periods of time may also lead to nozzleclogging. One countermeasure is to purge ceramic separation materialinto a wiping station every 2-10 layers, e.g., 5 layers, andalternatively or in addition purge 1 mm every time a tool change iscommanded, e.g., switching printing from the metal powder MIM compositenozzle to printing from the ceramic separation material nozzle within alayer.

The ceramic separation material loaded with a lower amount of powder,e.g., 15-35% by volume of powder, such as 25% powder, may tend to spreadout more during deposition, compared to the amount of spreading of ametal MIM material when printed. To address this, and to take advantageof the lesser spreading of the higher powder loaded MIM material, thelower-% ceramic separation material may be extruded in a layer onlyafter all or some of the metal material has been printed within thatlayer. Dimensional accuracy and the quality of the metal part isaffected less in this manner.

According to one embodiment, a sintering platform separated from thepart by a sinterable ceramic separation material reduces the amount ofsetter drag experienced by the part as the part slides on the sinterableceramic powder during shrinking and sintering, further reducing warpingand cracking.

Aspects in accord with the present invention are directed to a method of3D printing, comprising depositing a model material in successive layersto form a part, the model material being a metal composite includinggreater than 50% by volume metal powder and less than 50% by volume afirst removable binder, depositing the model material in successivelayers to form a support structure adjacent the part, depositing asinterable separation material between a surface of the part and asurface of the support structure, the sinterable separation materialformed from 10-40% by volume ceramic powder and greater than 50% byvolume a second removable binder, debinding the first removable binderof the model material and the second removable binder of the sinterableseparation material, and sintering the part, the support structure, andthe sinterable separation material at a temperature profile that sintersthe model material and the sinterable separation material.

According to one embodiment, the first removable binder and the secondremovable binder share more than 80% of their ingredients by volume.

According to another embodiment, the method further comprises depositingon a build plate the model material in successive layers to form ashrinking platform on which the part and the support structure areformed, and depositing a sliding release layer below the shrinkingplatform, the sliding release layer configured to remain powdered at asintering temperature of the model material and to promote slidingbetween the shrinking platform and the build plate during the sintering.

According to one embodiment, sintering the sinterable separationmaterial includes sintering the sinterable separation material such thatthe sinterable separation material becomes at least one of fragmented,cracked, flaked, and breakable after the sintering. In one embodiment,the method further comprises removing the sintered separation material.In another embodiment, removing the sintered separation materialincludes applying mechanical energy to the sintered separation materialand separating the sintered separation material from the part.

According to another embodiment, the method further comprises formingphysical connections between the part and the support structure, thephysical connections configured to remain in place throughout thesintering and to be separated from the part after the sintering byapplying mechanical energy. In one embodiment, the physical connectionsbetween the part and the support structure are formed from the modelmaterial. In another embodiment, the physical connections between thepart and the support structures are formed from the sinterableseparation material.

According to one embodiment, depositing the sinterable separationmaterial includes depositing the sinterable separation material with afirst nozzle having a lateral translation speed that is 10-75% of alateral translation speed of a second nozzle through which the modelmaterial is deposited.

According to another embodiment, the method further comprises depositingthe sinterable separation material in a wiping process in which a pathof deposition is retraced. In one embodiment, the method furthercomprises purging the sinterable separation material from a nozzle aftera predefined amount of the sinterable separation material has beendeposited.

According to one embodiment, depositing the model material within anyone of the successive layers includes depositing more than 50% of atotal amount of the model material to be deposited within the layerbefore depositing more than 50% of a total amount of the separationmaterial to be deposited within the layer. In one embodiment, depositingthe sinterable separation material includes depositing the sinterableseparation material formed from 15-35% by volume ceramic powder andgreater than 50% by volume the second removable binder.

Another aspect of the invention is directed to a method of 3D printing,comprising depositing a model material in successive layers to form apart, the model material being a metal composite including greater than50% by volume metal powder and less than 50% by volume a first removablebinder, depositing the model material in successive layers to form asupport structure adjacent the part, depositing a sinterable separationmaterial between a surface of the part and a surface of the supportstructure, the sinterable separation material formed from 10-40% byvolume ceramic powder and greater than 50% by volume a second removablebinder, debinding the first removable binder of the model material andthe second removable binder of the sinterable separation material, in afirst sintering mode, heating the part, the support structure, and thesinterable separation material at a sintering temperature that sintersthe model material while the ceramic powder of the sinterable separationmaterial remains as a debound powder, and in a second sintering mode,increasing the sintering temperature such that the debound powder of thesinterable separation material sinters to form sintered separationmaterial.

According to one embodiment, the first removable binder and the secondremovable binder share more than 80% of their ingredients by volume.

According to another embodiment, the method further comprises depositingon a build plate the model material in successive layers to form ashrinking platform on which the part and the support structure areformed, and depositing a sliding release layer below the shrinkingplatform configured to remain powdered at a sintering temperature of themodel material and to promote sliding between the shrinking platform andthe build plate during the first sintering mode and the second sinteringmode.

According to one embodiment, in the second sintering mode, increasingthe sintering temperature includes increasing the sintering temperaturesuch that the debound powder of the sinterable separation materialsinters and becomes at least one of fragmented, cracked, flaked, andbreakable after the second sintering mode. In one embodiment, the methodfurther comprises removing the sintered separation material. In anotherembodiment, removing the sintered separation material includes applyingmechanical energy to the sintered separation material to separate thesintered separation material from the part.

According to another embodiment, the method further comprises formingphysical connections between the part and the support structure, thephysical connections configured to remain in place throughout the firstsintering mode and the second sintering mode and to be separated fromthe part after the second sintering mode by applying mechanical energy.In one embodiment, the physical connections between the part and thesupport structure are formed from the model material. In anotherembodiment, the physical connections between the part and the supportstructures are formed from the sinterable separation material.

According to one embodiment, depositing the sinterable separationmaterial includes depositing the sinterable separation material with afirst nozzle having a lateral translation speed that is 10-75% of alateral translation speed of a second nozzle through which the modelmaterial is deposited.

According to another embodiment, the method further comprises depositingthe sinterable separation material in a wiping process in which a pathof deposition is retraced. In one embodiment, the method furthercomprises purging the sinterable separation material from a nozzle aftera predefined amount of the sinterable separation material has beendeposited.

According to one embodiment, depositing the model material within anyone of the successive layers includes depositing more than 50% of atotal amount of the model material to be deposited within the layerbefore depositing more than 50% of a total amount of the separationmaterial to be deposited within the layer. In one embodiment, depositingthe sinterable separation material includes depositing the sinterableseparation material formed from 15-35% by volume ceramic powder andgreater than 50% by volume the second removable binder.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic representation of three-dimensional metalprinter.

FIG. 1B is a schematic representation of a three-dimensional metalprinter, representing a binder jetting/powder bed printing approach.

FIG. 2 is a block diagram and schematic representation of athree-dimensional printer system.

FIG. 3 is a flowchart describing the overall operation of the 3D printerof FIG. 2.

FIG. 4 is a schematic representation of a 3D printing system, part, andprocess in which sintering supports (e.g., shrinking or densificationlinking supports) are provided.

FIGS. 5A-5D are schematic sections through the diagram of FIG. 4.

FIG. 6 is a schematic representation of an alternative 3D printingsystem, part, and process to that of FIGS. 4 and 5A-5D.

FIGS. 7A-C are schematic representations of exemplary processes ofprinting, debinding, sintering, and support removal with separationand/or release layers, green body supports and/or sintering or shrinkingor densification linking supports.

FIG. 8 is a schematic representation of an additional alternative 3Dprinting system, part, and process to that of FIG. 4.

FIG. 9 is a schematic representation of an additional alternative 3Dprinting system, part, and process to that of FIG. 4.

FIG. 10 is a top view of a sintered assembly of the 3D printing system,part, and process of FIG. 4, showing parting lines for removing supportshells or sintering or shrinking supports.

FIG. 11 is a top view of a sintered assembly of an alternative 3Dprinting system, part, and process to that of FIG. 4, showing partinglines for removing support shells or sintering or shrinking supports.

FIGS. 12 and 13 are, respectively, orthogonal and 3D/orthographic viewsof the part schematically depicted FIGS. 8 and 9.

FIGS. 14-16 are schematic views of a 3D printer in which filamentmaterials are configured in environmental conditions suitable forprinting.

FIG. 17 is a depiction of elastic modulus vs. temperature showing anappropriate range for maintaining a sinterable additive manufacturingfeedstock in a filament to permit spooling and transportation.

FIGS. 18-21 are schematic views of a 3D printers in which debinding maytake place as each layer is printed, or following each layer or a set oflayers.

FIG. 22 is a flowchart showing a method of depositing material to form asinterable brown part by additive manufacturing.

FIGS. 23A and 23B are alternative schematic representations of analternative 3D printing system, part, and process to that of FIGS. 4and/or 6.

FIG. 24 is a schematic representation of one exemplary process ofprinting, debinding, sintering, and support removal optionally withseparation and/or release layers, green body supports and/or fluidizedbed sintering.

FIG. 25 is a schematic representation of an additional exemplary processof sintering optionally with certain configurations of material andsintering oven.

FIG. 26A and FIG. 26B correspond to FIGS. 5B and 5D, respectively, andshow alternative selected sections through FIG. 4 for the purpose ofdiscussing printing and other process steps.

FIG. 26C and FIG. 26D are examples of respectively, hexagonal andtriangular honeycombs shown in cross section and employed as infill.

FIGS. 27 and 28 show side sectional views, substantially similar indescription to FIGS. 4, 6, 8 and 9, in which honeycomb cavities/infillare formed as vertical, columnar prism shapes.

FIG. 29 shows a side sectional view, substantially similar indescription to FIGS. 4, 6, 8, 9, 27, and 28 in which the distributionchannels cavities/infill are formed in an aligned, and/or angled, mannerthroughout the columnar prism shapes.

FIGS. 30 and 31 show a side sectional view, substantially similar indescription to FIGS. 4, 6, 8, 9, 27, 28 and 29, in which access channelsare provided.

FIG. 32 shows a chart in which the amount of shrinkage of the ceramicsintering support material should be more than that of the part modelmaterial until the final shrinkage amount is reached.

FIGS. 33A-33D, exaggerated in scale, show part shapes including eitheror both of convex or concave shapes (protrusions, cavities, orcontours).

FIGS. 34A and 34B show a flowchart and schematic, respectively, of agravity-aided debinding process useful with parts as described herein.

FIG. 35 shows a 3D printer for forming green parts from a curable ordebindable photopolymer.

FIGS. 36A and 36B show schematics representing deposition direction ofdeposition paths in retrograde patterns.

FIGS. 37A-37H, 37J are schematic views representing seam and jointinteraction in deposition walls and honeycombs.

FIGS. 38A and 38B show FDM/FFF nozzle assemblies in cross section.

FIGS. 39A and 39B show a MIM material extrusion nozzle assemblies incross-section.

FIG. 40 shows a MIM material extrusion nozzle assembly in cross-section.

DETAILED DESCRIPTION

This patent application incorporates the following disclosures byreference in their entireties: U.S. Patent Application Ser. Nos.61/804,235; 61/815,531; 61/831,600; 61/847,113; 61/878,029; 61/880,129;61/881,946; 61/883,440; 61/902,256; 61/907,431; and 62/080,890;14/222,318; 14/297,437; and Ser. No. 14/333,881, may be referred toherein as “Composite Filament Fabrication patent applications” or “CFFpatent applications”. Although the present disclosure discusses variousmetal or ceramic 3D printing systems, at least the mechanical andelectrical motion, control, and sensor systems of the CFF patentapplications may be used as discussed herein. In addition, U.S. Pat.Nos. 6,202,734; 5,337,961; 5,257,657; 5,598,200; 8,523,331; 8,721,032,and U.S. Patent Publication No. 20150273577, are incorporated herein byreference in their entireties. Further, U.S. Patent Application Nos.62/429,711, filed Dec. 2, 2016; 62/430,902, filed Dec. 6, 2016;62/442,395, filed Jan. 4, 2017; 62/480,331, filed Mar. 31, 2017;62/489,410, filed Apr. 24, 2017; 62/505,081, filed May 11, 2017;62/519,138, filed Jun. 13, 2017; 62/545,966, filed Aug. 15, 2017;62/575,219, filed Oct. 20, 2017; and Ser. No. 15/722,445, filed Oct. 2,2017 include related subject matter and are incorporated herein byreference in their entireties.

In 3D printing, in general, overhanging or jutting portions of a partmay require removable and/or soluble and/or dispersing supportsunderneath to provide a facing surface for deposition. In metalprinting, in part because metal is particularly dense (e.g., heavy),removable and/or soluble and/or dispersing supports may also be helpfulto prevent deformation, sagging, during mid- or post-processing—forexample, to preserve shape vs. drooping or sagging in potentiallydeforming environments like high heat.

Printing a sinterable part using a 3D printing material including abinder and a ceramic or metal sintering material is aided by supportstructures that are able to resist the downward pressure of, e.g.,extrusion, and locate the deposited bead or other deposition in space. Asinterable release layer intervening between the support structures andthe part includes a higher melting temperature material—ceramic or hightemperature metal, for example, optionally deposited with a similar(primary) matrix or binder component to the model material. The releaselayer does not sinter, and permits the part to “release” from thesupports. Beneath the sinterable release layer, the same model materialas the part is used for the support structures, promoting the samecompaction/densification during sintering. This tends to mean the partand the supports will shrink uniformly, maintaining dimensional accuracyof the part. At the bottom of the support, a sinterable release layermay also be printed. In addition, the support structures may be printedin sections with sinterable release layers between the sections, suchthat the final sintered support structures will readily break intosmaller subsections for easy removal, optionally in the presence ofmechanical or other agitation. In this way, a large support structurecan be removed from an internal cavity via a substantially smaller hole.In addition, or in the alternative, a further method of support is toprint soluble support material that is removed in the debinding process.For catalytic debind, this may be Delrin (POM) material.

One method to promote uniform shrinking or densification is to print aceramic release layer as the bottom most layer in the part. On top ofthe sliding release layer (analogous to microscopic ball bearings) athin sheet of metal—e.g., a raft—may be printed that will uniformlyshrink with the part, and provide a “shrinking platform” or“densification linking” platform to hold the part and the relatedsupport materials in relative position during the shrinking ordensification process. Optionally staples or tacks, e.g., attachmentpoints, connect and interconnect (or link as densification linking) themodel material portions being printed. The staples or tacks may beformed from part material (e.g. metal) or from intervening sinteringceramic support material.

The printer(s) shown herein with at least two print heads 18, 10 and/orprinting techniques, deposit with one head a composite materialincluding a binder and dispersed spheres or powder 18 (e.g., withinthermoplastic or curing binder), used for printing both a part andsupport structures, and with a second head 18 a (shown in FIGS. 4-9)deposits the release or separation material. Optionally a third headand/or fourth head include a green body support head 18 b and/or acontinuous fiber deposition head 10. A fiber reinforced compositefilament 2 (also referred to herein as continuous core reinforcedfilament) may be substantially void free and include a polymer or resinthat coats, permeates or impregnates an internal continuous single coreor multistrand core. It should be noted that although the print head 18,18 a, 18 b are shown as extrusion print heads, a “fill material printhead” 18, 18 a, 18 b as used herein may include optical or UV curing,heat fusion or sintering, or “polyjet”, liquid, colloid, suspension orpowder jetting devices—not shown—for depositing fill material, so longas the other functional requirements described herein are met.Functional requirements include one or more of employing green bodymaterial supports printing vs. gravity or printing forces; sintering orshrinking (densification linking) supports the part vs. gravity andpromote uniform shrinking via atomic diffusion during sintering; andrelease or separation materials substantially retain shape throughdebinding stems but become readily removable, dispersed, powderized orthe like after sintering. The sinterable separation material may becometacked, fragmented, cracked, flaked, or the like after sintering.

Although the Figures in general show a Cartesian arrangement forrelatively moving each print head in 3 orthogonal translationdirections, other arrangements are considered within the scope of, andexpressly described by, a drive system or drive or motorized drive thatmay relatively move a print head and a build plate supporting a 3Dprinted part in at least three degrees of freedom (i.e., in four or moredegrees of freedom as well). For example, for three degrees of freedom,a delta, parallel robot structure may use three parallelogram armsconnected to universal joints at the base, optionally to maintain anorientation of the print head (e.g., three motorized degrees of freedomamong the print head and build plate) or to change the orientation ofthe print head (e.g., four or higher degrees of freedom among the printhead and build plate). As another example, the print head may be mountedon a robotic arm having three, four, five, six, or higher degrees offreedom; and/or the build platform may rotate, translate in threedimensions, or be spun. The print bed or build plate, or any other bedfor holding a part, may be moved by 1, 2, or 3 motors in 1, 2, or 3degrees of freedom.

A long or continuous fiber reinforced composite filament is fullyoptional, and when used, is fed, dragged, and/or pulled through aconduit nozzle optionally heated to a controlled temperature selectedfor the matrix material to maintain a predetermined viscosity, force ofadhesion of bonded ranks, melting properties, and/or surface finish.After the matrix material or polymer of the fiber reinforced filament issubstantially melted, the continuous core reinforced filament is appliedonto a build platen 16 to build successive layers of a part 14 to form athree-dimensional structure. The relative position and/or orientation ofthe build platen 16 and print heads 18, 18 a, 18 b, and/or 10 arecontrolled by a controller 20 to deposit each material described hereinin the desired location and direction. A driven roller set 42, 40 maydrive a continuous filament along a clearance fit zone that preventsbuckling of filament. In a threading or stitching process, the meltedmatrix material and the axial fiber strands of the filament may bepressed into the part and/or into the swaths below, at times with axialcompression. As the build platen 16 and print head(s) are translatedwith respect to one another, the end of the filament contacts an ironinglip and be subsequently continually ironed in a transverse pressure zoneto form bonded ranks or composite swaths in the part 14.

With reference to FIG. 1A, 1B through 40, each of the printheads 18, 18a, 18 b, 10 may be mounted on the same linear guide or different linearguides or actuators such that the X, Y motorized mechanism of theprinter moves them in unison. As shown, each extrusion printhead 18, 18a, 18 b may include an extrusion nozzle with melt zone or meltreservoir, a heater, a high thermal gradient zone formed by a thermalresistor or spacer (e.g., stainless steel, glass, ceramic, optionally anair gap), and/or a Teflon or PTFE tube. A 1.75-1.8 mm; 3 mm; or largeror smaller thermoplastic (and/or binder matrix) filament is driven via,e.g., a direct drive or a Bowden tube drive, and provides extrusion backpressure in the melt reservoir.

FIG. 1B shows in schematic form a binder jetting powder bed printer,with some components generally similar to the extrusion printer of FIG.1A. The printer 1000J includes two or more print heads 18 (jetting orapplying a binder to bind powder 132 to form model material or boundcomposite), 18 a (jetting or extruding release or separation material),and or 18 b (jetting or extruding placeholder material) supplied bysupply lines 142. The printer 1000J may deposit with print head 18 abinder 132 upon the powder bed 134 to form a composite materialincluding a debinder and dispersed spheres or powder (metal or ceramicpowder), used for printing a part, support structures, and a shrinkingor densification linking platform. A sinterable powder feedstockreservoir, supply or refill 136 supplies the powder bed 134 with newlayers of unbound powder, which is leveled by a leveling or doctor roll138. Excess from leveling is captured in a feedstock overflow reservoir140. With a second head 18 a, the printer 1000J may deposit release orseparation material. Optionally the third head and/or fourth headinclude the placeholder material head 18 b and/or a continuous fiberdeposition head 10 as described herein. The binder jetting printer 1000Jdescribed herein meets the functional requirements described herein(e.g., green body and/or placeholder material supports printing vs.gravity or printing forces, sintering supports support the part vs.gravity and promote uniform shrinking via atomic diffusion duringsintering, and release or separation materials substantially retainshape through debinding steps but become readily removable, dispersed,powderized or the like after sintering, or in the case of sinteringseparation material, tacked, fragmented, cracked, flaked, or the likeafter sintering.

FIG. 2 depicts a block diagram and control system of thethree-dimensional printers, e.g., in FIGS. 1A and 1B, which controls themechanisms, sensors, and actuators therein, and executes instructions toperform the control profiles depicted in and processes described herein.A printer is depicted in schematic form to show possible configurationsof e.g., three commanded motors 116, 118, and 120. It should be notedthat this printer may include a compound assembly of printheads 18, 18a, 18 b, and/or 10.

As depicted in FIG. 2, the three-dimensional printer 3001 (alsorepresentative of printer 1000 and 1000J) includes a controller 20 whichis operatively connected to any fiber head heater 715 or similar tipheater, the fiber filament drive 42 and the plurality of actuators 116,118, 120, wherein the controller 20 executes instructions which causethe filament drive 42 to deposit and/or compress fiber into the part.The instructions are held in flash memory and executed in RAM (notshown; may be embedded in the controller 20). An actuator 114 forapplying a spray coat (including a spray release powder), as discussedherein, may also be connected to the controller 20. In addition to thefiber drive 42, respective filament feeds 1830 (e.g., up to one each forheads 18, 18 a, and/or 18 b) may be controlled by the controller 20 tosupply one or more extrusion printheads 18, 18 a, 18 b, 1800. Aprinthead board 110, optionally mounted on the compound printhead andmoving therewith and connected to the main controller 20 via ribboncable, breaks out certain inputs and outputs. The temperature of theironing tip 726 may be monitored by the controller 20 by a thermistor orthermocouple 102; and the temperature of the heater block holding nozzleof any companion extrusion printhead 1800 may be measured by respectivethermistors or thermocouples 1832. A heater 715 for heating the ironingtip 726 and respective heater(s) 1806 for heating respective extrusionnozzles 18, 18 a, 18 b, 1802 are controlled by the controller 20. Heatsink fan(s) 106 and a part fan(s) 108, each for cooling, may be sharedbetween the printheads, or independently provided per printhead, andcontrolled by the controller 20. A rangefinder 15 that measures adistance from the printhead assembly to the part (and thereby a surfaceprofile of the part) is also monitored by the controller 20. The cutter8 actuator, which may be a servomotor, a solenoid, or equivalent, isalso operatively connected to the controller 20. A lifter motor forlifting one or any printhead away from the part (e.g., to controldripping, scraping, or rubbing) may also be controlled by the controller20. Limit switches 112 for detecting when the actuators 116, 118, 120have reached the end of their proper travel range are also monitored bythe controller 20.

As depicted in FIG. 2, an additional breakout board 122, which mayinclude a separate microcontroller, provides user interface andconnectivity to the controller 20. An 802.11 Wi-Fi transceiver connectsthe controller to a local wireless network and to the Internet at largeand sends and receives remote inputs, commands, and control parameters.A touch screen display panel 128 provides user feedback and acceptsinputs, commands, and control parameters from the user. Flash memory 126and RAM 130 store programs and active instructions for the userinterface microcontroller and the controller 20.

FIG. 3 depicts a flowchart showing a printing operation of the printers1000 in FIGS. 1A through 40. FIG. 3 describes, as a coupledfunctionality, control routines that may be carried out to alternatelyand in combination use the co-mounted FFF extrusion head(s) 18, 18 a,and/or 18 b and/or a fiber reinforced filament printing head as in theCFF patent applications.

In FIG. 3, at the initiation of printing, the controller 20 determinesin step S10 whether the next segment to be printed is a fiber segment ornot, and routes the process to S12 in the case of a fiber filamentsegment to be printed and to step S14 in the case of other segments,including e.g., base (such as a raft or shrinking/densification linkingplatform), fill (such as extruded or jet-bound model material, releasematerial, or placeholder material), or coatings (such as sprayed orjetted release material). After each or either of routines S12 and S14have completed a segment, the routine of FIG. 3 checks for slicecompletion at step S16, and if segments remain within the slice,increments to the next planned segment and continues the determinationand printing of fiber segments and/or non-fiber segments at step S18.Similarly, after slice completion at step S16, if slices remain at stepS20, the routine increments at step S22 to the next planned slice andcontinues the determination and printing of fiber segments and/ornon-fiber segments. “Segment” as used herein corresponds to “toolpath”and “trajectory”, and means a linear row, road, or rank having abeginning and an end, which may be open or closed, a line, a loop,curved, straight, etc. A segment begins when a printhead begins acontinuous deposit of material, and terminates when the printhead stopsdepositing. A “slice” is a single layer, shell or lamina to be printedin the 3D printer, and a slice may include one segment, many segments,lattice fill of cells, different materials, and/or a combination offiber-embedded filament segments and pure polymer segments. A “part”includes a plurality of slices to build up the part. Support structuresand platforms also include a plurality of slices. FIG. 3's controlroutine permits dual-mode printing with one, two, or more (e.g., four)different printheads, including the compound printheads 18, 18 a, 18 b,and/or 10. For example, the decision at S10 may be a “case” structurewhich proceeds to different material printing routines in addition toS12, S14.

All of the printed structures previously discussed may be embeddedwithin a printed article during a printing process, as discussed herein,expressly including reinforced fiber structures of any kind, sparse,dense, concentric, quasi-isotropic or otherwise as well as fill material(e.g., including model material and release material) or plain resinstructures. In addition, in all cases discussed with respect toembedding in a part, structures printed by fill material heads 18, 18 a,18 b using thermoplastic extrusion deposition may be in each casereplaced with soluble material (e.g., soluble thermoplastic or salt) toform a soluble preform which may form a printing substrate for partprinting and then removed. All continuous fiber structures discussedherein, e.g., sandwich panels, shells, walls, reinforcement surroundingholes or features, etc., may be part of a continuous fiber reinforcedpart. The 3D printer herein discussed with reference to FIGS. 1A-40 maythereby deposit either fill material (e.g., composite with a debindablematrix containing metal, ceramic, and/or fibers), soluble (e.g.,“soluble” also including, in some cases, debindable by thermal,pyrolytic or catalytic process) material, or continuous fiber. Withreference to FIGS. 1 and 2, each of the printheads 18 and 10 are mountedon the same linear guide such that the X, Y motorized mechanism 116, 118of the printer 1000 moves them in unison. A 1.75-1.8 mm; 3 mm or largeror smaller metal filament 10 b may be driven through, e.g., direct driveor a Bowden tube that may provide extrusion back pressure in a meltreservoir 10 a or crucible.

Commercially valuable metals suitable for printing include aluminum,titanium and/or stainless steel as well as other metals resistant tooxidation at both high and low temperatures (e.g., amorphous metal,glassy metal or metallic glass). One form of post-processing issintering. By molding or 3D printing model material as described herein,a green body may be formed from an appropriate material, including abinder or binders and a powdered or spherized metal or ceramic (ofuniform or preferably distributed particle or sphere sizes). A brownbody may be formed from the green body by removing one or more binders(e.g., using a solvent, catalysis, pyrolysis). The brown body may retainits shape and resist impact better than the green body due to remeltingof a remaining binder. In other cases the brown body may retain itsshape but be comparatively fragile. When the brown body is sintered athigh temperature and/or pressure, remaining or second stage binder maypyrolyse away, and the brown body substantially uniformly contracts asit sinters. The sintering may take place in an inert gas, a reducinggas, a reacting gas, or a vacuum. Application of heat (and optionally)pressure eliminates internal pores, voids and microporosity between andwithin the metal or ceramic beads through at least diffusion bondingand/or atomic diffusion. Supporting material, either the same ordifferent from model material, supports the part being printed,post-processed, or sintered versus the deposition force of printingitself (e.g., green body supports) and/or versus gravity (e.g., greenbody supports or sintering supports), particularly for unsupportedstraight or low-angle spans or cantilevers.

Printing a part is aided by the support structures, able to resist thedownward pressure of, e.g., extrusion, and locate the deposited bead ordeposition in space. As discussed herein a sinterable release layerprinted from a separation material feedstock includes a higher meltingtemperature and/or sintering temperature powdered material—ceramic forexample, optionally deposited in or via a similar (primary) matrixcomponent to the model material. Beneath the sinterable separationlayer, sinterable tacks, or sinterable tack layer, the same (metal)material is used as the part, promoting the samecompaction/densification. This tends to mean the part and the supportswill shrink uniformly, maintaining overall dimensional accuracy of thepart. At the bottom of the sintering support, a sinterable separationlayer, sinterable tacks, or sinterable tack layer may also be printed.In addition, the sintering support structures may be printed sectionswith sinterable layers, tacks such that the final sintered supportstructures will readily break into smaller subsections for easy removal,optionally in the presence of mechanical or other agitation. In thisway, a large support structure can be removed from an internal cavityvia a substantially smaller hole. In addition, or in the alternative, afurther method of support is to print soluble support material that isremoved in the debinding process. For catalytic debind, this may beDelrin (POM) material. One method to promote uniform shrinking is toprovide (potentially print) a ceramic rolling or sliding layer ofpowdered material as the bottom most layer in the part. On top of thesliding release layer (analogous to microscopic ball bearings) a thinsheet of metal—e.g., a raft—may be printed that will uniformly shrinkwith the part, and provide a “shrinking platform” or “densificationlinking platform” to hold the part and the related support materials inrelative position during the shrinking or densification process.Optionally staples or tacks, e.g., attachment points (e.g., either orboth of metal tacks or sintering ceramic tacks) connect and interconnectthe model material portions being printed.

As noted, in one example, green body supports may optionally be printedfrom a matrix of thermal, soluble, or catalytic debindable compositematerial (e.g., catalytic including Polyoxymethylene—POM/acetal) andhigh melting point metal (e.g., molybdenum) or ceramic spheres, andleave behind a sinterable powder when debound. In another example, greenbody supports are printed from a thermal, soluble, pyrolytic orcatalytically responsive material (e.g., polymer or polymer blend) andleave behind only removable byproducts (gases or dissolved material)when the green body supports are removed. The green body supports may beformed to be mechanically or chemically or thermally removed before orafter debinding, but preferably are also made from thermal, soluble,pyrolytic or catalytically responsive material, and may be fully removedduring the debinding stage (or immediately thereafter, e.g., subsequentpowder cleaning to remove the remaining sinterable powder). In somecases, the green body supports are removed by a differentchemical/thermal process from the debinding, before or after debinding.

An exemplary catalytically debindable composite material including POMor acetal is one example of a two-stage debinding material. In somecases, in a two-stage debinding material, in a first stage a firstmaterial is removed, leaving interconnected voids for gas passage duringdebinding. The first material may be melted out (e.g., wax),catalytically removed (e.g., converted directly into gas in a catalyticsurface reaction), or dissolved (in a solvent). A second stage binder,e.g., polyethylene, that is not as responsive to the first materialprocess, remains in a lattice-like and porous form, yet maintaining theshape of the 3D printed object awaiting sintering (e.g., before themetal or ceramic balls have been heated to sufficient temperature tobegin the atomic diffusion of sintering). This results in a brown part,which includes, or is attached to, the sintering supports. As the partis sintered at high heat, the second stage binder may be pyrolysed andprogressively removed in gaseous form.

FIGS. 4 through 7 show, in schematic form, additional explanation ofrelevant processes, structures, materials, and systems. As shown inFIGS. 4-7, a 3D printer 1000 suitable for the deposition phase of theprocess may include one, two, three, or more deposition heads 18, 18 a,18 b for depositing model material and supports (as well as, e.g., acontinuous composite deposition head 10, not shown in FIGS. 4-7). Asshown in FIG. 4, a model material deposition head 18 deposits acomposite material including metal or ceramic spherized powder as wellas a meltable or matrix of binding polymers, waxes, and/or other utilitycomponents. In the model material deposition head 18, the process mayuse a low-diameter filament (e.g., 1-4 mm) as both material supply andto provide back pressure for extrusion. In this case, the model materialextrusion filament supplied to head 18 may be stiff, yet reasonablypliable as supplied (e.g., 0.1-3.0 GPa flexural modulus) and reasonablyviscous when fluidized (e.g., melt or dynamic viscosity of 100-10,000Pa·s, preferably 300-1000 Pa·s) in order to support bridging whileprinting across gaps or spans, even absent green body supports orsintering (i.e., shrinking or densification linking) supports below.

In the 3D printer 1000 and exemplary part 14 shown in FIG. 4, asinterable separation or release material deposition head 18-S (or 18 a)and a green body support material deposition head 18-G (or 18 b, thegreen body support material also or alternatively being a placeholdermaterial) may additionally be supported to move in at least threerelative degrees of freedom with respect to the part P1 being printed asdiscussed with reference to FIGS. 1A-3 inclusive. As discussed herein,the separation feedstock or material may in some cases serve as a greenbody support, so alternatively, as shown in FIG. 6, only one head 18-SGmay deposit both green body support material and sinterable separationmaterial. As shown in FIG. 4, from bottom to top (in this case, 3Dprinting is performed from the bottom up), in these exemplary processesthe first layer provided (optionally printed) may be a raft separationlayer or sliding release layer SL1 printed from, e.g., a powderedseparation material deposition head 18-S (or 18-SG). This material maybe, as noted herein, of similar debinding materials to the modelmaterial, but, e.g., with a ceramic or other spherical powder filler(e.g., particulate) that remains powdered at the sintering temperatureof the model material. Consequently, the separation material may haveits debinding material completely removed by solvent, catalysis,pyrolysis, leaving behind a dispersible and/or removable powder (e.g.,after sintering, the powder of the separation material remainingunsintered even after the sintering process). In the case of sinterableseparation material, the material becomes tacked, fragmented, cracked,flaked, breakable into shards with impact or the like after sintering.“Separation” and “release” are generally used interchangeably herein.

FIGS. 5A-5D show selected sections through FIG. 4 for the purpose ofdiscussing printing and other process steps. It should be noted that theFigures are not necessarily to scale. In particular, very smallclearances or material-filled clearances (e.g., separation or releaselayers) or components (e.g., protrusions for snap removal) may be shownat exaggerated scales for the purpose of clear explanation. Moreover, itshould also be noted that in some cases, solid bodies are shown tosimplify explanation, but the internal structure of the solid bodiesherein may be 3D printed with porous, cellular, or hollow infillpatterns (e.g., honeycombs) and/or may include chopped, short, long, orcontinuous fiber reinforcement as discussed in the CFF PatentApplications.

As shown in FIGS. 4 and 5A, upon an optionally removable andtransportable, optionally ceramic build plate 16, a raft separationlayer SL1 is provided (e.g. by a non-printing mechanism or by hand) orprinted by separation material head 18-S to permit a raft or shrinkingplatform or densification linking platform RA1 printed above to bereadily removed from the build plate 16, in some cases before debinding,or in some cases when the (e.g., portable) build plate 16 itself isstill attached through the debinding process (in the example shown inFIG. 7A).

As shown in FIGS. 4 and 5B, following the printing of the raftseparation layer SL1, a raft or shrinking platform or densificationlinking platform RA1 of model material (e.g., metal-bearing composite)is printed. The raft or shrinking platform RA1 is printed, e.g., for apurpose of providing a continuous model material foundation or materialinterconnection among the part and its supports, so that the process ofmass transport and shrinking/densification during sintering is uniformlycarried out, e.g., about a common centroid or center of mass, e.g.,“densification linking”. The raft RA1 may serve other purposes—e.g.,improving early adhesion, clearing environmentally compromised (e.g.,wet, oxidized) material from an extrusion or supply path, orconditioning printing nozzles or other path elements (e.g., rollers) toa printing state, etc. As noted, two general classes of supports may beused: green body supports GS1, GS2 (which support the part being printedduring the printing process, but are removed before or during sintering)and sintering (e.g., shrinking or densification linking) supports SS1,SH1, RA1 (which support the part being sintered during the sinteringprocess). Green body support GS2 also may be used to “placehold”internal volumes, either holes or cavities in the part shape itself orinternal honeycomb cavities. Some supports may serve both roles. Asshown in FIGS. 4 and 5B, should an upper portion of the entire printbenefit from green body supports, the lower layers of green bodysupports GS1 may be printed upon either the build plate 16, or as shownin FIGS. 4 and 5B, upon the sinterable separation layer SL1 and/or theraft or shrinking platform RA1.

As shown in FIGS. 4 and 5C, subsequently, the raft or shrinking platformRA1 may be continued up into or connected up to a surrounding or lateralshell support structure SH1 (either contiguously or via a parting linePL and/or physical separation structure, e.g., a pinched and/orwasp-waisted and/or perforated or otherwise weakened cross-section thatmay be flexed to break away). Further, separation structures—in thiscase model material protrusions P1 (or similarly formed sinterableceramic tacks or protrusions) as well as an optionally interveningseparation layer SL2 formed as sintering ceramic tacks, tack layer, orlayer—may be printed between the raft RA1 and shell SH1 to permit theremoval of the raft RA1 and shell SH1 subsequent to sintering.Protrusions P1 described herein, facing vertical, horizontal, or otherdirection, may be formed to be snapped by sharp or pulsed impact(s),e.g., having a contact surface cross-section of less than ½ mm. Theprinting of green body supports GS1 is continued upwards, in this caseproviding printing support to optionally angled (e.g., 10-45 degreesfrom vertical), sparse and/or branching sintering (e.g., shrinking ordensification linking) supports SS1 printed to later provide sinteringsupport for an overhanging or cantilevered portion OH1, as well asbuilding up a green body support GS1 for printing support for the sameoverhanging or cantilevered portion OH1. “Printing support” as usedherein may mean support vs. printing back pressure or gravity duringprinting, while “sintering support” may mean support vs. gravity,support vs. other external/internal stress during sintering, as well asor alternatively meaning providing interconnections facilitating evenlydistributed mass transport and/or atomic diffusion. Although anoverhanging or cantilevered portion OH1 is show in FIG. 4, anunsupported span even if contiguous to the part P1 at two opposingsides, may also benefit from supports as described.

As shown in FIGS. 4 and 5D, the surrounding shell support structure SH1is continued up printing in layers, and optionally interconnectedvertically or diagonally to the part 14 via, e.g., protrusions P1 ofmodel material or sintering ceramic tack material connected to the shellsupport structure SH1, and/or separation layer material SL2 material.The parting lines and separation structures similarly are continuedvertically, preserving the planes along which they will be removed. Aninternal volume V1 in the part P1, in this case a cylindrical volume V1,is printed with green body supports GB2—if the model material issufficiently viscous or shape-retaining during printing, the 3D printingprocess may bridge gaps or diagonally stack, and internal volumes withsloping walls or arch-like walls may not require sintering supports.Alternatively, the internal volume V1 is printed with sinteringsupports, or a combination of green body supports GB# and sinteringsupports SS#, e.g., as with the supports SS1 below overhang OH1. Theinternal volume V1 is printed with a channel to the outside of the partto permit support material to be removed, cleaned away, or more readilyaccessed by heat transfer or fluids or gasses used as solvents orcatalysis. The green body supports GS1 and branching sintering supportsSS1 are similarly continued to later provide sintering support for anoverhanging or cantilevered portion OH1, as well as building up a greenbody support GS1 for printing support for the same overhanging orcantilevered portion OH1.

As shown in FIGS. 4 and 5D, an overhang or cantilevered portion OH1 maybe supported by sintering supports SS1 at an angle, so long as thesintering supports SS1 are self-supporting during the printing processe.g., either by the inherent stiffness, viscosity, or other property ofthe model material as it is printed in layers stacking up at a slightoffset (creating the angle), or alternatively or in addition with thelateral and vertical support provided by, e.g., the green body supportsGS1. The sintering supports SS1 must also be robust to remain integralwith the part 14 or supporting the part 14 through the sinteringprocess. Any of the sintering supports SS1 shown in FIG. 5C or 5D mayalternatively be vertical columns or encased by a columnar sinteringsupport encasing structure deposited from model material.

Finally, as shown in FIG. 4, the remainder of the part 14, support shellstructure SH1, sintering (e.g., shrinking or densification linking)supports SS1, and green body supports GS1, GS2 are printed tocompletion. As printed, essentially all portions of the part 14 whichrequire printing or sintering support are supported in a verticaldirection either via green body supports GS1, GS2, sintering (e.g.,shrinking or densification linking) supports SS1, the raft RA1,separation layer SL1 and/or SL2. Portions of the part 14, or structureswithin the part 14 that are self-supporting (because, e.g., of thematerial properties of the model material composite, or external bodiesproviding support, and/or those which are sufficiently stiff duringsupport removal, debinding, and/or sintering) need not be supported vs.gravity. In addition, the support structures SS1, the raft RA1, and/orthe shell structure SH1 are interconnected with model material to thepart 14 in a manner that tends to shrink during sintering about a samecentroid or center of mass or at least maintain relative local scalewith respect to the neighboring portion of the part 14. Accordingly,during the approximately 12-24% (e.g., 20%) uniform shrinking ordensification of the sintering process, these support structures shrinkor densify together with the part 14 and continue to provide support vs.gravity.

FIG. 6 shows a variation of the 3D printer, printing method, partstructure, and materials of FIG. 4. In FIG. 6, no separate green bodysupport deposition head 18 c (or 18-G) is provided. Accordingly, greenbody supports GS1, GS2 and sinterable separation layers SL1, S12 areformed from the same material—e.g., the composite material used forsinterable separation layers, in which a ceramic or high-temperaturemetal particles or spheres are distributed in an, e.g., one-stage ortwo-stage debindable matrix. In this case, the green body supports GS1,GS2 are not necessarily removed during or before debinding or in aseparate process, but are instead simply weakened during debinding and,as with the sinterable separation layers, have their remaining polymermaterial pyrolysed during sintering. Sintered remaining ceramic (and/oradditional unsintered ceramic powder) can be cleaned out and/or removedfollowing sintering, at the same time as the separation layers. In thecase of sintering separation material, tacks, fragments, cracked, flakesor shards can be cleaned out and/or removed and/or broken for removalvia impact or following sintering, at the same time as the separationlayers.

FIG. 7A shows one overall schematic of the process. Components in FIG.7A correspond to those of the same appearance labeled in FIG. 4, but arenot labeled in FIG. 7A so that different steps may be shown. Initially,in the 3D printing phase, the part 14, together with its green bodysupports GS, sintering supports SS, and sinterable separation layers SL(as described and shown in FIG. 4), is printed in a 3D printer asdescribed. The green body, including all of these support structures(e.g., a green body assembly GBA), and optionally still bound orconnected to a ceramic or other material build plate 16, is transferredto a debinding chamber (optionally, the debinding chamber is integratedin the 3D printer 1000 or vice versa). As noted, if the green bodysupports are made of a different polymer, binder or substance than thefirst stage debinding material, a separate process may remove the greenbody supports before debinding. If the green body supports are made fromeither the same or similar substances as the first stage debindingmaterial, or one that responds to the same debinding process bydecomposing or dispersing, the green body supports may be removed duringdebinding. Accordingly, as shown in FIG. 7A, debinding includes removinga first binder component from the model material using a thermalprocess, a solvent process, a catalysis process, or a combination ofthese, leaving a porous brown body structure (“DEBINDING”), and mayoptionally include dissolving, melting, and/or catalyzing away the greenbody supports (“SUPPORT REMOVAL 1”).

Continuing with FIG. 7A, as shown, a brown body (e.g., a brown bodyassembly BBA with the attached sintering support and/or surroundingshell) is transferred to a sintering chamber or oven (optionallycombined with the printer and/or debinding chamber). The brown body,e.g., as a brown body assembly BBA, includes the part, optionally asurrounding shell structure, and optionally sintering supports. Asnoted, the surrounding shell structure and sintering (e.g., shrinking ordensification linking) supports are different aspects of sinteringsupport structure. Optionally, intervening between the shell structureand/or sintering supports are sinterable separation layers, formed from,e.g., the sinterable separation material. Optionally, interveningbetween the shell structure and/or sintering supports are protrusions orridges of model material interconnecting these to the part, and/orsinterable ceramic tacks, protusions or ridges interconnecting the partto the supports. Optionally, the same or a similar separation materialintervenes between the brown body (e.g., as brown body assembly) and thebuild plate. During sintering, the brown body (e.g., as a brown bodyassembly) uniformly shrinks by approximately 12-24%, such as 20%,closing internal porous structures in the brown body (e.g., as a brownbody assembly) by atomic diffusion. The second stage debinding componentof the model material may be pyrolysed during sintering (including, forexample, with the assistance of catalyzing or other reactive agents ingas or otherwise flowable form).

As shown in FIG. 7A, a sintered body (e.g., as a sintered body assembly)can be removed from the sintering oven. The supporting shell structureand the sintering supports can be separated or broken up along partinglines, and/or along sinterable separation layers, and or by snapping orflexing or applying an impact to protrusion connections, tacks or otherspecifically mechanically weak structures (including sintered ceramictacks, tack layer, protrusions, ridges, and/or layer). The separationlayers are brittle, partially or completely sintered, and are readilyremoved. Should the green body supports be formed from the separationmaterial, the green body supports are similarly brittle, sinterable andmay be readily removed.

FIG. 7B shows a variation of the process shown in FIG. 7A, where thesintered part is removed from a sintered support structure composed of ametal material scaffold that maintains the height and shape of thesupport while the bulk of the support structure is composed of thesintering ceramic material. Both components shrink with the part. Theremoval process requires the application of a mechanical energy to thepart. The shock of the applied energy needs to be sufficient to breakthe material along the parting line, this energy can be between 0.1-100joules, or more optimally 0.3-7 Joules and applied to the base of thesupport or any region of the support structure large enough to directthe mechanical energy to the interfacial layer.

FIG. 7C shows a variation of the process shown in FIGS. 7A and 7B. Thesintering ceramic support material that does not maintain it's shapethrough the sintering process and instead collapses to form a powderduring the mid-stages of the sintering process which then partially orcompletely sinters into an easily removable flake during the finalstages of the sintering process. The metal scaffold provides thestructural and shrinking support while the sintering ceramic materialthat is trapped between the metal scaffold and the part preventsexcessive tacking of the part to the support structure. Subsequentcleaning may remove remainder powder or tacks, fragments, shards, orflakes.

FIG. 8 shows a variation of a part printed as in FIG. 4 or FIG. 6. Thepart shown in FIG. 8 includes four overhanging or cantilevered sectionsOH2-OH5. Overhang OH2 is a lower, thicker overhang under a cantilevered,thinner overhang OH3. While the lower overhang OH2 may in some cases beprinted without sintering supports or even green-body supports as aself-supporting cantilever, it is below the long cantilever overhangOH3, which is sufficiently long, thin, and heavy that it may requireboth green body supports and sintering supports. Overhang OH4 is adownward-leaning overhang, which generally must be printed with at leastgreen body supports (because its lowest portion is otherwiseunsupported, i.e., in free space, during printing) and in a formdifficult to remove sintering supports printed beneath without draftingor parting lines (because rigid sintering supports would become lockedin). Overhang OH5 is a cantilever including a heavy block of modelmaterial, which may require both green body and sintering support. Inaddition, the part shown in FIG. 8 includes an internal, e.g.,cylindrical volume V2, from which any necessary sintering supports mustbe removed via a small channel. For reference, the 3D shape of the part14 of FIG. 8 is shown in FIGS. 12 and 13.

As shown in FIG. 8, in contrast to the sintering supports SS1 of FIGS. 4and 6, sintering (e.g., shrinking or densification linking) supportsSS2, supporting overhangs OH2 and OH3, may be formed including thinwalled, vertical members. These vertical members form vertical channelswhich, as described herein, may permit fluid flow for debinding. Thevertical members of sintering supports SS2 may be independent (e.g.,vertical rods or plates) or interlocked (e.g., accordion or meshstructures). As shown in FIG. 8, the sintering supports SS2 (or indeedthe sintering supports SS1 of FIGS. 4 and 6, or the sintering supportsSS3, SS4, and SS5 of FIG. 8) may be directly tacked (e.g., “tacked” maybe contiguously printed in model material, but with relatively smallcross-sectional area) to a raft RA2, to the part 14 a, and/or to eachother. Conversely, the sintering supports SS2 may be printed above,below, or beside a sinterable separation layer, without tacking. Asshown, the sintering supports SS2 are removable from the orthogonal,concave surfaces of the part 14 a.

Further, as shown in FIG. 8, similar sintering (e.g., shrinking ordensification linking) supports SS3 are printed beneath thedownward-leaning overhang OH4, and beneath heavier overhang OH5. Inorder that these supports SS3, may be readily removed, some or all areprinted with a parting line PL, e.g., formed from sinterable separationmaterial, and/or formed from a mechanically weakened separationstructure (e.g., printing with a nearly or barely abutting clearance asdescribed herein, or printing with a wasp-waisted, pinched, orperforated cross-section, or the like), or a combination of these (or,optionally, a combination of one or both of these with green bodysupport material having little or no ceramic or metal content, shouldthis be separately printed). These material or mechanical separationstructures, facilitating removal of the sintering supports, may besimilarly printed into the various sintering supports shown in FIGS.4-7, 9, and throughout.

In addition, as shown in FIG. 8, sintering (e.g., shrinking ordensification linking) supports SS5 are printed within the internalvolume V2. The sintering supports SS5 are each provided with multipleparting lines, e.g., printed in a plurality of separable segments, sothat the sintering supports in this case can be broken or fall apartinto parts sufficiently small to be readily removed, via the channelconnecting the internal volume V2. As shown, the channel CH2 itself isnot printed with internal supports, as an example of a small-diameterhole of sufficient rigidity during both printing and sintering to holdits shape. Of course, supports may be printed of either or both types inchannel CH2 to ensure shape retention.

FIG. 9 is substantially similar to FIG. 8, but shows some variations instructure. Both variations in printing with and without reinforcementare shown, e.g., while FIG. 9 shows reinforcement structures CSP1therein, the remaining variant structures in the solid bodies, supports,and separation layers of FIG. 9 are optionally applicable to thenon-reinforced structures of FIG. 8 and throughout. For example, beneathoverhang OH3, a monolithic, form-fitting shell SH3 is printed of modelmaterial, separated from the part 14 by either release or separationlayers SL2 and/or protrusions P1. The monolithic shell SH3 has smallopen cell holes throughout to lower weight, save material, and improvepenetration or diffusion of gases or liquids for debinding. As discussedherein, open cell holes may optionally be connected to access and/ordistribution channels for debinding fluid penetration and draining,e.g., any of the structures of FIGS. 25-31 may form, be formed by or becombined with the open cell holes. This shell SH3 may surround the part14 if sufficient parting lines or release layers are printed into theshell SH3 (e.g., instead of the structures SH4 and SH5 to the left ofthe drawing, a similar structure would be arranged), and if sufficientlyform following, act as a workholding piece.

In another example in FIG. 9, monolithic (e.g., lateral) support (e.g.,shrinking or densification linking) shell SH4 is printed integral withthe raft RA2, but with a parting line PL angled to draft and permitremoval of the support shell SH4. In a further example shown in FIG. 9,support shell SH4 is printed angled upward (to save material) and with alarge cell or honeycomb interior to lower weight, save material, and/orimprove penetration or diffusion of gases or liquids for debinding. FIG.9 also shows examples of continuous fiber layers deposited by, e.g.,continuous fiber head 10. Sandwich-panel reinforcement layers CSP1 arepositioned at various layers, e.g., within upper and lower bounds ofoverhangs OH2, OH3, and OH5.

As shown in FIGS. 4 through 9, sintering supports SS1, SS2, SS3 may beformed in blocks or segments with at least some intervening releaselayer material, so as to come apart during removal. In any of theseFigures and throughout, supports may be tacked or untacked. “Untacked”sintering supports may be formed from the model material, i.e., the samecomposite material as the part, but separated from the part to beprinted by a release layer, e.g., a higher temperature composite havingthe same or similar binding materials. For example, for most metalprinting, the release layer may be formed from a high temperatureceramic composite with the same binding waxes, polymers, or othermaterials. The release layer may be very thin, e.g., one 3D printinglayer. When the metal is sintered, the release layer—having already hada first stage binder removed—is essentially powderized as thetemperature is insufficient to sinter or diffusion bond the ceramicmaterial. This enables the untacked sintering supports to be easilyremoved after sintering. Or, for example, the release layer may beformed from a sinterable ceramic composite with the same binding waxes,polymers, or other materials. The release layer may be very thin, e.g.,one 3D printing layer. When the metal is sintered, the sinterablerelease layer—having already had a first stage binder removed—issintered as the temperature is sufficient to sinter or diffusion bondthe ceramic material. In this case the sintered ceramic forms a brittlerelease layer. This enables the untacked sintering supports to be easilyremoved after sintering.

In the case of a sinterable release layer—having already had a firststage binder removed—the sinterable release layer is sintered as thetemperature is sufficient to sinter or diffusion bond the ceramicmaterial. In this case the sintered ceramic forms a brittle releaselayer. This enables the untacked sintering supports to be easily removedafter sintering.

“Tacked” sintering supports, in contrast, may be similarly formed fromthe model material, i.e., the same composite material as the part, butmay connect to the part either by penetrating the release layer orwithout a release layer. The tacked sintering supports are printed to becontiguous with the part, via thin connections, i.e., “tacked” at leastto the part. The tacked sintering supports may in the alternative, or inaddition, be printed to be contiguous with a raft below the part thatinterconnects the part and the supports with model material. The raftmay be separated from a build plate of a 3D printer by a layer or layersof release layer material (including, for example, sinterable releasematerial).

The tacks themselves may be separately formed from the sintering ceramicsupport material.

A role of tacked and untacked of sintering supports is to providesufficient supporting points versus gravity to prevent, or in some casesremediate, sagging or bowing of bridging, spanning, or overhanging partmaterial due to gravity. The untacked and tacked sintering supports areboth useful. Brown bodies, in the sintering process, may shrink byatomic diffusion, e.g., uniformly about the center of mass or centroidof the part. In metal sintering and some ceramics, typically this is atleast in part solid-state atomic diffusion. While there may be somecases where diffusion-based mass transport among the many interconnectedmetal/ceramic spheres does not transport sufficient material to, e.g.,maintain a very thin bridge joining large masses, this is notnecessarily the case with supports, which may be contiguously formedconnected at only one end as a one-ended bridge (or connected at twoends as two-ended bridges; or interconnected over the length).

In those cases where tacked sintering supports are tacked to, orconnected to, or linked to, a model material raft or shrinking platformor densification linking platform upon which the part is printed, theinterconnection of model material among the tacked sintering supports(and/or sintering ceramic tacks, tack layer, or layer) and the raft canbe arranged such that the centroid of the raft-supports contiguous bodyis at or near the same point in space as that of the part, such that thepart and the raft-support contiguous to the part each shrink duringsintering uniformly and without relative movement that would move thesupports excessively with respect to the part. In other cases, the partitself may also be tacked to the model material raft, such that theentire contiguous body shrinks about a common centroid. In anothervariation, the part is interconnected to the raft via tacked sinteringsupports tacked at both ends (e.g., to the raft and to the part) orand/along their length (e.g., to the part and/or to each other). Thetacks themselves may be separately formed from the sintering ceramicsupport material.

In other cases, untacked sintering supports may be confined within avolume and contiguous with the raft and/or the part, the volume formedfrom model material, such that they may shrink about their own centroids(or interconnected centroid) but are continually moved through space andkept in a position supporting the part by the surrounding modelmaterial. For example, this may be effective in the case of the internalvolume V2 of FIG. 8 or 9.

In the alternative, or in addition, support or support structures orshells may be formed from model material following the form of the partin a lateral direction with respect to gravity, e.g., as shown incertain cases in FIGS. 4-9. The model material shells may be printedtacked to the base raft (which may be tacked to the part). They may beprinted integral with, but separable from the base raft. The base raftmay be separable together with the model material shells. These supportstructures may be offset from or substantially follow the lateral outercontours of the part, or may be formed from primitive shapes (straightor curved walls) but close to the part. In one variation, the supportstructures may envelop the part on all sides (in many cases, includingparting lines and/or separation structures to permit the shell to beremoved). These offset support structures may be printed with asinterable separation layer or layers of the sinterable separationmaterial (optionally sinterable ceramic or another material that willtransfer mechanical support but will not be difficult to separate).

These offset support structures may be, in the alternative or inaddition, printed with a sinterable separation layer or layers of thesinterable separation material (optionally sinterable ceramic or anothermaterial that will transfer mechanical support but will not be difficultto separate).

Any of the support structures discussed herein—e.g., tacked or untackedsintering supports, and/or support shells, may be printed with, insteadof or in addition to intervening separation material, a separationclearance or gap (e.g., 5-100 microns) between the part and supportstructure (both being formed from model material). In this manner,individual particles or spheres of the support structure mayintermittently contact the part during sintering, but as the separationclearance or gap is preserved in most locations, the support structuresare not printed with compacted, intimate support with the part. When andif bonding diffusion occurs at intermittently contacting particles, theseparation force required to remove the separation clearance supportstructures after sintering may be “snap-away” or “tap-away”, and in anycase far lower (e.g., 1/10 or lower force) than an integral orcontiguous extension of the part. Larger separation clearances or gaps(e.g., 200-300 microns) may permit debinding fluid to penetrate and/ordrain.

In an alternative, separation gaps or clearances between the part andsupport structures may be placed in partial segments following thecontour, with some of the remainder of the support structures followingthe e.g., lateral contour of the part more closely or more distantly, orboth. For example, support structures may be printed with a smallseparation gap (5-100 microns) for the majority of the supportstructure, but with other sections partially substantially following thecontour printed yet closer to the part (e.g., 1-20 microns) providingincreased rigidity and support during sintering, yet generally over aset of limited contact areas (e.g., less than 5% of contact area),permitting removal. This may also be carried out with large and mediumgaps (e.g., 100-300 microns separation for the larger clearance supportstructures, optionally with separation material intervening, and 5-100microns for the more closely following support structures). Further,this may be carried out in three or more levels (e.g., 100-300 microngaps, 5-100 micron gaps, and 1-20 micron gaps in different portions ofthe support structures following the contour of the part).

Optionally, the sintering support structures may include a followingshell with an inner surface generally offset from the e.g., lateral partcontour by a larger (e.g., 5-300 microns) gap or clearance, but willhave protrusions or raised ridges extending into the gap or clearance toand separated by the smaller gap (e.g., 1-20 microns), or extendingacross the gap or clearance, to enable small point contacts between thepart and support structures formed from the same (or similar) modelmaterial. Point contacts may be easier to break off after sintering thancompacted, intimate contact of, e.g., a following contour shell.Optionally, a neat matrix (e.g., green body supports formed from one ormore of the binder components) support structure may be printed betweenmodel material (e.g., metal) parts and model material (e.g., metal)support structures to maintain the shape of the part and structuralintegrity during the green and brown states, reducing the chance ofcracking or destruction in handling.

While several of the Figures are shown in side, cross section view, FIG.10 shows the sintered body structure of FIG. 4 in top views, while FIG.11 shows a variation for the purpose of explanation. As shown, supportshells or other structures may be printed with separation or partinglines or layers between portions of the support structure. Theseparation or parting lines or layers may be any separation structuredescribed herein, including those described between the part and supportstructure. For example, the separation lines or layer permitting asupport shell to be broken into two or more parts (optionally manyparts) may be formed from separation material (e.g., ceramic andbinder), from binder material, from model material (e.g., metal) withseparation gaps (such as 1-20, 5-100, or 50-300 microns) and/orprotrusions or ridges permitting snap-off structures. For example, asupport structure or shell may be formed to be split in two halves(e.g., as in FIG. 10), creating a parting line in the support structureor shell. Parting lines are optionally printed to be contiguous within aplane intersecting (e.g., bisecting) a support shell structure so as topermit ready separation. Multiple planes of parting lines may intersectthe support shell structure. A “parting line”, “parting surface”, and“parting plane” are used herein similarly to the context in injectionmolding—the plane along which one structure separates from another, forgenerally a similar reason—permitting the part-surrounding structures tobe removed without interference with or entrapment in the part. While inthe context of injection molding these terms refer to the plane alongwhich mold halves separate, in the present disclosure the term “parting”line, surface, or structure refers to the plane along which supportstructures supporting or enveloping a part may break or segment orseparate from one another.

In the case of complex geometries, as noted above, support structuresmay be printed with parting lines, sectioned into smaller subsections(e.g., as PL-1 in FIG. 11, like orange slices, or further sectioned inan orthogonal axis such that they can be easily removed), as shown inFIG. 11. For example, if support structures are printed filling in adovetail of a part, support structures could be formed in three parts,e.g., could be designed in three parts, such that the center part eitherhas draft or is rectangular and can be easily removed, thereby freeingup the two side parts to slide inward and then be removed. Conversely,parting lines may be printed to be interlocking (e.g., PL-3 in FIG. 11),crenellated or formed as a box joint (e.g., similar to PL-3 in FIG. 11),so as to resist separation, in some cases other than in a transversedirection. Parting lines may be printed nearly almost cut through thesupport shell (e.g., PL-2 in FIG. 11). Note that FIG. 11 is depictedwithout protrusions P1, i.e., with only separation layers SL2 in thevertical direction, and largely monolithic, surrounding support shellSH.

In some cases, particularly in the case of a small number of partinglines (e.g., halves, thirds, quarters) the support structures, at leastbecause they are form following structures, may be preserved for lateruse as a workholding fixture, e.g. soft jaws, for holding a sintered thepart in secondary operations (such as machining). For example, if asupport structure were to support a generally spherical part, a supportstructure suitable for later use as a workholding jaw or soft jaw, thestructure should retain the part from all sides, and therefore extendpast the center or half-way point of the sphere. For the purposes ofsintering and supporting vs. gravity, the support structure need notextend past the halfway point (or slightly before), but for the purposesof subsequent workholding for inspection and post processing, thesupport structure would continue past the half way point (e.g. up to ⅔of the part's height, and in some cases overhanging the part) enablingpositive grip in, e.g., a vise.

Further, attachment features to hold the workholding fixture(s) or softjaw(s) in a vise (or other holder) may be added to the support structurefor the purpose of post processing, e.g., through holes for attachmentto a vise, or dovetails, or the like. Alternatively, or in addition, aceramic support may be printed, and sintered, to act as a reusablesupport for the sintering step of many 3D printed parts. In this case,upwardly facing surfaces of the reusable support may be printed toshrink to the same height as the matching or facing surface of the partbeing supported.

Accordingly, in a method of depositing material and an apparatus foradditive manufacturing, the apparatus feeds a first filament including abinder matrix and sinterable spherized and/or powdered first materialhaving a first sintering temperature along a material feed path, andfeeds a second filament including the binder matrix and sinterablespherized and/or powdered second material having a second sinteringtemperature higher than the first sintering temperature (optionally,e.g., more than 500 degrees C. higher). The apparatus forms layers ofsecond material by deposition upon a build plate or prior deposition offirst or second material, and layers of first material by depositionupon prior deposition of second material. The apparatus (including anadditional station of the apparatus) debinds at least a portion of thebinder matrix from each of the first material and second material. Theapparatus (including an additional station of the apparatus) then heatsa part so formed from first and second material to the first sinteringtemperature, thereby sintering the first material and decomposing thesecond material. In printing a sinterable part using a 3D printing modelmaterial including a binder and a sinterable ceramic or metal sinteringmaterial, a sinterable release layer intervenes between supportstructures and the part, each of the support structures and the partformed of the model material or composite. The sinterable release layerincludes a spherized or powdered higher melting temperaturematerial—ceramic or high temperature metal for example, optionallydeposited with a similar (primary) matrix or binder component to themodel material.

As discussed herein, a feedstock material for forming the part and/orthe sintering supports may include approximately 50-70% (preferablyapprox. 60-65%) volume fraction secondary matrix material, e.g.,(ceramic or metal) substantially spherical beads or powder in 10-50micron diameter size, approximately 20-30% (preferably approx. 25%volume fraction of soluble or catalysable binder, (preferably solid atroom temperature), approximately 5-10% (preferably approx. 7-9%) volumefraction of pyrolysable binder or primary matrix material, (preferablysolid at room temperature), as well as approximately 0.1-15% (preferablyapprox. 5-10%) volume fraction of carbon fiber strands, each fiberstrand coated with a metal that does not react with carbon at sinteringtemperatures or below (e.g., nickel, titanium boride). As discussedherein, the “primary matrix” is the polymer binder and is deposited bythe 3D printer, holding the “secondary matrix” beads or spheres and thefiber filler; and following sintering, the (ceramic or metal) materialof the beads or spheres becomes the matrix, holding the fiber filler.

Alternatively, a feedstock material for forming the part and/or thesintering supports may include approximately 50-70% (preferably approx.60-65%) volume fraction secondary matrix material, e.g., (ceramic ormetal) substantially spherical beads or powder in 10-50 micron diametersize (in another embodiment 0.04-10 micron diameter size), approximately20-30% (preferably approx. 25% volume fraction of soluble or catalysablebinder, (preferably solid at room temperature), approximately 5-10%(preferably approx. 7-9%) volume fraction of a pyrolysable binder orsecondary matrix material approximately 1/10- 1/200 the elastic modulusof the (ceramic or metal) secondary matrix material, and approximately0.1-15% (preferably approx. 5-10%) volume fraction of particle or fiberfiller of a material approximately 2-10 times the elastic modulus of thesecondary, (metal or ceramic) matrix material. As discussed herein, the“primary matrix” is the polymer binder and is deposited by the 3Dprinter, holding the “secondary matrix” beads or spheres and the fiberfiller; and following sintering, the (ceramic or metal) material of thebeads or spheres becomes the matrix, holding the particle of fiberfiller.

A comparison of elastic modulus may be found in the following table,with polymer/binder primary matrices of 1-5 GPa elastic modulus

Secondary Elastic Modulus Elastic Modulus matrix (10⁹ N/m², GPa) Fill(10⁹ N/m², GPa) Steel 180-200 Carbon Fiber 200-600 Aluminum  69 GraphiteFiber 200-600 Copper 117 Boron Nitride 100-400 Titanium 110 BoronCarbide  450 Alumina 215 Silicon Carbide  450 Cobalt 209 Alumina  215Bronze  96-120 Diamond 1220 Tungsten Carbide 450-650 Graphene 1000Carbon Nanotube  1000+

The spheres, beads or powder (e.g., particulate) may be a range ofsizes. A binder may include dispersant, stabilizer, plasticizer, and/orinter-molecular lubricant additive(s). Some candidate secondarymatrix-filler combinations that may be deposited by a 3D printer withina binder or polymer primary matrix include cobalt or bronze beads withtungsten carbide coated graphite (carbon) fibers; aluminum beads withgraphite (carbon) fibers; steel beads with boron nitride fibers;aluminum beads with boron carbide fibers; aluminum beads with nickelcoated carbon fibers; alumina beads with carbon fibers; titanium beadswith silicon carbide fibers; copper beads with aluminum oxide particles(and carbon fibers); copper-silver alloy beads with diamond particles.Those fibers that may be printed via the techniques of the CFF PatentApplications may also be embedded as continuous fibers. Carbon forms forparticles or fibers include carbon nanotubes, carbon blacks,short/medium/long carbon fibers, graphite flakes, platelets, graphene,carbon onions, astralenes, etc.

Some soluble-pyrolysable binder combinations include polyethylene glycol(PEG) and polymethyl methacrylate (PMMA) (stearic acid optional, PMMA inemulsion form optional); waxes (carnauba, bees wax, paraffin) mixed withsteatite and/or polyethylene (PE); PEG, polyvinylbutyral (PVB) andstearic acid. Some pyrolysable second stage binders include: polyolefinresins polypropylene (PP), high-density polyethylene (HDPE); linearlow-density polyethylene (LLDPE), and polyoxymethylene copolymer (POM).As noted, in thermal debinding, a part containing binder is heated at agiven rate under controlled atmosphere. The binder decomposes by thermalcracking in small molecules that are sweep away by the gas leaving theoven. In solvent debinding, a part containing binder is subject todissolving the binder in appropriate solvent, e.g., acetone or heptane.In catalytic debinding, the part is brought into contact with anatmosphere that contains a gaseous catalyst that accelerates cracking ofthe binder, which can be carried away.

FIG. 14 is a schematic view of a 3D printer in which filament materialsare configured in environmental conditions suitable for printing. Whenbinder materials include at least polymer materials and/or waxes, thebehavior of the polymers and/or waxes for the purposes of feeding andback pressure during printing may be temperature dependent, even at roomtemperature (e.g., 20 degrees C.) and mildly elevated operatingtemperatures (e.g., above 20 degrees C. but below 80 degrees C.). Withincreasing temperature, stiffness decreases and ductility increases.When temperature increases to approach a softening or glass transitiontemperature, elastic modulus changes at a higher rate. For an amorphouspolymer, the elastic modulus and load-bearing ability becomes negligibleabove the glass transition temperature TG-A (as shown in FIG. 17). For asemi-crystalline material, a small amount (e.g., ⅓- 1/10 of elasticmodulus below Tg) of stiffness or elastic modulus may remain mildlyabove the glass transition temperature TG-SC (shown in FIG. 17),continuing to decrease to the melting point. Binder materials—whetherpolymer or wax or both—may have more than one component, and one or moreglass transition temperatures or melting temperatures, and a glasstransition temperature Tg marks a significant softening. FIG. 17 showsone possible spool temperature span for one possible polymer or waxcomponent such as the softening materials discussed herein. However, itshould be noted that the particular position on this curve relative tothe noted glass transition temperature TG of a component is lessimportant than the feeding behavior of the filament as a whole—thefilament should be softened from any brittle state sufficiently to bepulled or drawn off the spool without breaking, yet hard enough to befed by an extruder, and sufficiently pliable to be bent repeatedlywithin the Bowden tubes BT1 and, e.g., cable carrier EC1.

In a composite material including >50% metal or ceramic spheres, as wellas a two stage binder, advantageous mechanical properties for 3Dprinting, debinding and sintering (including melt viscosity, catalyticbehavior and the like) may result in a printing material that—whilehaving properties suitable or advantageous for other parts of theprocess, may be claylike and/or brittle at room temperature, even thoughthe material becomes suitably fluidized but also suitably viscous andself-supporting for 3D printing when at a printing temperature (aboveone or more glass transition temperatures or melting temperatures of thematerial).

Suitable structures for handling materials brittle at room temperatureare shown in FIGS. 14-16, 3D printers schematically depicted andotherwise constructed similarly to FIGS. 1-9. FIGS. 14 and 15 may acceptspools of model material and/or release material (as discussed herein,composite material that may be sintered after debinding, or, for releasematerial, that contains high temperature particles or spheres thatresist powderize when a binder portion is pyrolysed during sintering)that were wound at a temperature higher than room temperature but lessthan a glass transition temperature of a binder material, e.g., 50-55degrees Celsius, for example with an approximately 1.75 mm diameterfilament. Optionally, the temperature is comparable to the glasstransition or softening temperature of a wax component of the modelmaterial, but lower than the glass transition or softening temperatureof a polymer component. As shown in FIGS. 14 and 16, spools kept warmmay include the model material and the release material, and these maybe in a joint heated chamber (HC1) heated by a heater HT1. The heaterHT1 keeps the spools at the 50-55 degrees Celsius contemplated by thisexample, for example with an approximately 1.75 mm diameter filament.The build plate 16 may be heated by a build plate heater 16 a, whichmaintains roughly a similar temperature (e.g., 50-55 degrees Celsius)during printing, and also helps maintains the temperature within theprinting compartment at a level above room temperature. A smallerdiameter filament may be softened sufficient for bending and feeding ata lower temperature (e.g., for a 1 mm filament, 40-45 degrees may beemployed).

Each spool/material may be kept in its own independent chamber ratherthan the joint chamber HC1, and each may be heated by its own heaterrather than the joint heater HT1. Heater HT1 may be a passive, e.g.,radiant and convection heater, or include a blower. As shown in FIGS.14-16, a return channel RC1 or path may permit air to be drawn into theheated chamber HC1 from the printing compartment, and the blower-typeheater may keep the heated chamber HC1 at a comparative positivepressure. If the heated chamber HC1 is sufficiently sealed except forthe return channel RC1 as an inlet and the filament outlets and Bowdentubes BT1 downstream from the driving “extruders” EXT1 (e.g.,rubber-wheeled or steel-wheeled filament drive systems), the heated airwithin the heated chamber HC1 may be driven through the Bowden tubes BTsurrounding the driven filaments to maintain the temperature at anelevated level as the warmed filament is moved through the Bowden tubesand, in some cases, flexed during printing. At least the driven air andthe heater 16 a heating the build plate may maintain the printingcompartment and the air returned via channel RC1 at a higher than roomtemperature level (and reduce energy consumption). In order that thebending radius of the Bowden tubes, and therefore the filament inside,are kept controlled, a segmented cable carrier (e.g., energy chain) thatmaintains a minimum bending radius EC1 may house the Bowden tubes.

FIGS. 14-16 differ in the orientation of the spools and the drivingsystem of the filament. In FIG. 14, spools are horizontally arranged ona lazy-susan type holder that permits rotation, and the filament drivers(including their, e.g., elastomer drive wheels) are arranged at aconvenient location mid-way between the spools and the Bowden tubes.This mid-drive arrangement is suitable if the filament is not softenedto an elastomer range in the heating chamber HC1. In FIG. 15, the spoolsare vertically arranged in a rotating spool holder (e.g., on rollers),and the filament drivers or “extruders” (including their driving wheels,e.g., of elastomer) are arranged directly upstream of the melt chamberin the respective nozzles 18, 18 a. This direct drive arrangement issuitable for softer as well as stiffer filaments. In FIG. 16, the spoolsare vertically arranged on an axle, and the filament, and the filamentdrivers or “extruders” (including their driving wheels, e.g., ofelastomer) are arranged directly upstream of the melt chamber in therespective nozzles 18, 18 a. Moreover, in FIG. 16, the heated chamber isa large volume, and the filament is dropped substantially directly downto the moving printing heads 18, 18 a so as to have a large bend radiusin all bends of the filament (e.g., as shown, no bend more of smallerthan a 10 cm bend radius, or, e.g., no bend radius substantially smallerthan that of the spool radius). Bowden tubes guide the filaments forpart of the height leading up to the spools.

In one alternative embodiment, rather than debinding an entire partafter printing, at least a portion of the debinding is performed whileor after printing layers of the part and/or supports. As discussedherein, debinding may be performed by solvent, heating and/or applyingvacuum evaporation or sublimation, catalysis, or other means of removingor decomposing a binder, in each case removing at least a part of thematrix material for subsequent processes such as sintering. It may bemore advantageous to debind less than a layer at a time (e.g., with adirected debinding head optionally travelling with the print head) or alayer, a few layers, or several layers at a time (e.g., with afull-enclosure debinding system or a region-at-a-time or scannabledebinding system).

Full part molding technologies using debinding, in contrast to additiveor 3D printing technologies, necessarily apply debinding processes to afull molded part. As discussed herein, full part debinding is similarlyuseful for additive or 3D printed parts as well, and may offeradvantages versus molded parts in the case of additive or 3D printedparts (e.g., weight may be reduced and/or debinding accelerated wheninternal honeycomb, access channels, open cells, and other debindingacceleration structures are printed).

In contrast, layer-by-layer debinding (e.g., not limited to one layer ata time—continuous debinding while printing, or debinding part of a layerat a time, or debinding a set of layers are each possible) may haveunique advantages in the case of 3D printed or additive technologies. Aswith molding, a purpose of a first stage binder in the case of extrusion3D printing (e.g., using spooled or coiled filament, spooled or foldabletapes, or feedable rods) is delivery of the sinterable powder into thedesired shape, while a purpose of a second stage binder is adhesion andshape retention in the brown part versus gravity and system/processforces. After delivery, the first stage binder need only be retained solong as is necessary or useful for adhesion and shape retention versusthese forces. In the case of molding, this would be at least until afterthe green part is formed, and in most cases until after the green partis removed from the mold. In the case of 3D printing, depending on thedebinding system and binder material properties, the binder can beremoved substantially immediately after deposition (e.g., if some firststage binder remains, and/or a second stage binder or other componentretains structural integrity versus gravity and printing/processingforces). If sufficient structural integrity remains, a debinding headmay continuously debind “behind” a deposited road that has solidified,or even one that has not yet solidified or cooled to solidification. Asanother example, a debinding head may independently track or scan aportion of a layer, a full layer, or a set of layers; or a volumetric orbulk process (e.g., heating, vacuum) in the printing chamber maycontinuously debind or debind in duty cycles. In all of these cases ofsubstantially layer-by-layer debinding, several advantages result.Significantly, the process of debinding is accelerated because internalsurfaces are directly available for debinding. Similarly, structuresimpractical to debind in full-part process (e.g., dense or large parts)may be debound. No additional time or transport is necessary followingprinting, as the printer continuously transforms (continuously, regionby region, layer by layer, or layer set by layer set) green layers ofthe part into brown layers, and a printed part is a brown part. Evenpartial debinding may accelerate the overall process by increasing theavailable surface area for whole part debinding. For example, a partialdebinding sweep may be conducted upon a printed layer or set of layers,temporarily exposing some surfaces to debinding fluid (gas or liquid).

FIGS. 18-21 are schematic views of a 3D printers in which debinding maytake place as each layer is printed, or following each layer or a set oflayers. The printer of FIGS. 18-21 accepts spools of model materialand/or release material that are either temperature controlled to bepliable when heated above room temperature, or are pliable at roomtemperature; or alternatively discrete rod material fed by an, e.g.,piston feeder. The build plate 16 may be heated by a build plate heater16 a, which may maintain a temperature during printing which contributesto debinding (e.g., elevated, but below a fluidizing or softeningtemperature of the model material and may maintains the temperaturewithin the printing compartment at a level above room temperature (theprinting compartment also in addition or alternatively use a separateheater, not shown, for this purpose). As shown in FIGS. 18-21, at leastthe heater 16 a heating the build plate, with the optional assistance ofa chamber heater HT2, may maintain the printing compartment at a higherthan room temperature level, and a segmented cable carrier (e.g., energychain) that maintains a minimum bending radius EC1 may house Bowdentubes as well as air, gas, fluid and/or vacuum lines for fumeextraction.

In one example, as shown in FIG. 18, each of the print heads 180, 180 aincorporates at least a print head (for extruding or spraying modelmaterial, green body support material, or sintering support material)and a debinding head DBH1 (for debinding a first stage binder fromprinted model material). The type of debinding head DBH1 depends uponthe debinding process for the first stage binder material. For example,a debinding head DBH1 for thermally debindable first material mayinclude one or both of a forced hot air gun or a radiant or IR heatelement or projector. In the case of a material debound in a vacuum(increasing a vapor pressure of the binder), the entire chamber may beunder vacuum (e.g., by means of a vacuum pump or high-vacuum apparatusconnected by vacuum conduit VC1) as well; and in the case of a materialdebound in a particular gas (inert or active), the entire chamber may befilled with such gas via inert atmosphere port ATM1. A debinding headDBH1 for a solvent or catalytically debindable first material mayinclude a spray, droplet, or jet of solvent or catalyst fluid, aerosol,or gas (optionally warmed, heated, or recycled). In either case, thedebinding head DBH1 may include or add a waste or fume collection vacuumor extractor FE1. An additional head-borne or whole chamber process mayaccelerate (e.g., by gas flow, vacuum, or heat) removal of the debindingsolvent following the debinding step.

In the case of a heat gun or radiant element, the layer or road of firstmaterial deposited may be heated to temperature of 200-220 degrees C. todebind the material. Optionally, the fume extractor FE1 or vacuum may beconcentric or partially concentric with a heat source, such that fumesare extracted similarly without dependence on the direction of travel ofthe debinding head DBH1. Similarly, the debinding head DBH1, with orwithout the fume extractor FE1, may be concentric with the printing head180 or 180 a, again so that debinding may “follow” or track the printhead 180 or 180 a in any direction, and/or may perform similarly in anyCartesian direction of movement. Alternatively, either of the debindinghead DBH1 or the fume extractor FE1 may be mounted onto a side of theprint head 180 or 180 a (with or without independent articulation fordirection) and may be mounted on a separately or independently movablecarriage. In each case described herein (concentric, adjacent, or mainscan) the fume extractor FE1 is preferably proximate to an output of thedebinding head DBH1 (e.g., spray, heat radiator, etc.), e.g., no morethan 0.1-10 mm from the debinding head DBH1.

Alternatively, as shown in FIG. 19, the debinding head DBH1 is afull-width main scan debinding head, mount on a separate carriage thattravels the width of the printer in a sub scan, and has an optionaltrailing and/or leading fume extractors FE1. This main-scan debindinghead DBH1 may debind the entire layer in one or more passes. The mainscan debinding head DBH1 may be arranged at a predetermined and/oradjustable clearance from each layer, e.g., such that its output (e.g.,heat radiator) faces the part with an, e.g., clearance of 0.1-10 mm, andmay avoid blowing air which may perturb fine printed features.

Further alternatively, as shown in FIG. 20, the debinding head DBH1includes a directable, coherent, or highly collimated radiation beamemitter (e.g., laser) in the debinding head DBH1, fixedly mounted with aline of sight of the useful print bed 16, or on a separate carriage thattravels at least in part to allow line of sight or positioning at anappropriate focus distance; or mounted on the print head DBH1 to movewith it similarly to FIG. 18. A beam emitting debinding head DBH1 maydebind continuously, road by road, or an entire layer in one or morepasses. The preferred power level of the beam or laser may be similar toSLS lasers used for plastic (e.g., 100 mW-100 W). In each implementationin FIGS. 18-21 discussed herein, the print bed 16 and/or the chamber maybe elevated by heaters 16 a and/or HT2 to a temperature near thedebinding temperature (e.g., 1-10 degrees below) so that a heat-based orheat-using debinding head DBH1, e.g., beam emitter, need elevate thetemperature of the part layer by only a few degrees in order to performthe debinding process; or may be elevated by heaters 16 a and/or HT2 toa temperature (e.g., 90-150 degrees C.) that partially debinds the layeror continues to debind the layers below the current layer. In eachimplementation in FIGS. 18-21 discussed herein, a warm air jet, ambientair jet or cooled air jet may follow or otherwise track the debindinghead DBH1 to cool the layer following debinding, and/or return it to theoperating temperature of the environment (which may be overall orpartially elevated).

Still further alternatively, as shown in FIG. 21, upon completion of alayer, the part may be lowered (e.g., slightly or completely) into asolvent bath (e.g., circulated, recirculated, agitated and/or heated).In this case, the debinding head DBH1 may be considered the solvent bathstructure; and debinding 1-5 layers at a time may be a more effectiveapproach because of the raising/lowering time. In each example in FIGS.18-21, a fume extractor FE1 may remove dissolved, volatile, atomized,fluidized, aerosolized or otherwise removed binder. The fume extractorFE1 may be connected to a pump which directs the collected material intoa cold trap CT1 (e.g., to condense volatile, sublimated, or gas statematerial to liquid or solid material) and optionally thereafter througha carbon filter or other gas cleaner CF1 before exhausting to anappropriate outlet. A fume extractor FE2 separate from the debindinghead DBH1 may evacuate or remove fumes from the entire chamberseparately.

As shown in FIG. 22, the present disclosure describes a method ofdepositing material to form a sinterable brown part by and an apparatusfor additive manufacturing may include making a raft RA1 in step S40.Subsequently, as discussed herein, in Step S42 a layer, portion of alayer, or set of layers is printed, and in Step S44 the layer is deboundas discussed with reference to FIGS. 18-21 and throughout thisdisclosure. This process is repeated—noting that dense printing mayresult in more frequent debinding steps. When all the layers are bothprinted and debound, as in step S46, the process is complete. The methodmay include feeding along a material feed path. The apparatus feeds afirst filament including a binder matrix and sinterable spherized and/orpowdered first material having a first sintering temperature, e.g., themodel material. A green layer of first material is deposited orpartially deposited, at least in some cases upon a brown layer of firstmaterial that has already been debound. In other cases it may bedeposited upon a layer of sintering support or green body supportmaterial. At least a portion of the binder matrix is then removed fromthe green layer or portion thereof of first material to debind eachgreen layer into a corresponding brown layer. When all the green layershave been both printed and converted into brown layers, the part is abrown part and may be sintered the part at the first sinteringtemperature.

When sintering supports are used, the apparatus (and/or process) mayinclude a second print head along a material feed path, and theapparatus can feed a second filament including the binder matrix andsinterable spherized and/or powdered second material having a secondsintering temperature higher than the first sintering temperature(optionally, e.g., more than 300, or more than 500 degrees C. higher).The apparatus forms layers of the second material—the separation layermaterial—which may have a second sintering temperature more than 300degrees C., or more than 500 degrees C. higher than the first sinteringtemperature. Green layers of model material are deposited upon a bydeposition upon a build plate or prior deposition of a brown layer(previously debound layer-by-layer as discussed herein) or separationmaterial, and at least a portion of the binder matrix from each greenlayer is debound to convert that layer or layers into a correspondingbrown layer. Layers of the separation material are deposited upon abuild plate or first or second material, and layers of first material bydeposition upon prior deposition of model material or separationmaterial as appropriate, to permit sintering supports to be laterremoved or build up separation material. When all brown layers of thepart have been so converted, the part may be sintered at the firstsintering temperature but below the second material. The apparatus(including an additional station of the apparatus) debinds at least aportion of the binder matrix from each of the first material and secondmaterial. The apparatus (including an additional station of theapparatus) then heats a part so formed from first and second material tothe first sintering temperature, thereby sintering the first materialwithout sintering and decomposing the second material (the separationmaterial) The second stage binder in the separation material, is,however pyrolysed, leaving an unsintered powder behind.

In the present disclosure, a vacuum-assisted debinding process using ahigh vapor pressure first stage binder subject to sublimation (e.g.,naphthalene) may be particularly effective in the case whereinterconnected channels are printed. The 3D printing model material mayinclude a binder and a ceramic or metal sintering material, and arelease layer intervenes between infill cells or honeycomb or open cellsin the part interior that connect to support structures and the partexterior. As discussed herein, open cell holes may optionally form, beformed by, or be connected to access and/or distribution channels fordebinding fluid penetration and draining. “Vacuum-assisted” may meandebinding in gaseous pressure below ambient, optionally below 0.1-5 mmHg, where any remaining gas may be air or inert, with or without addedheat by a debinding head, heated printbed, and/or heatedprinting/debinding chamber. All or some, each of the channels/holes maybe sized to remain open during debinding under vacuum, yet close duringthe approximately 20% size (approximately 20% may be 12-24%) reductionor densification of sintering. In such a case, the first stage bindermay include chemically compatible solid, liquid and/or paste-like higherhydrocarbon and ester binder components having a measurable vaporpressure at the low end of the debinding temperatures (supportstructures and thus readily removable), especially under reducedpressure and elevated temperature conditions, prior to or without theuse of extracting solvents. Preferably, such total or partial waxreplacement components in the binder fraction would be characterized bya low-lying triple point which would make the removal of the componentfeasibly by sublimation, i.e., directly from the solid into the vaporphase, and thus preserving the open structure of the polyolefin binderphase.

In the present disclosure, binder compositions suitable for roomtemperature filament winding, commercial range shipping, and roomtemperature storage and unspooling may be formed by combining lowmelting point waxes and other compatible materials into a first stagebinder. A problem to be overcome is brittleness, which prevents bendingor winding of relatively high-aspect ratio filament (e.g., 1-3 mm)without breaking.

Solvent-debinding MIM feedstocks often include three distinctcomponents. One component is the solvent-extractable partially misciblelower molecular weight component, such as petroleum wax (PW),microcrystalline wax (MW), crystalline wax (CW), bee's wax, C15-C65paraffins and the like. The first stage binder component may serve as apore former that can be rapidly and conveniently removed from the greenpart without changing its dimensions and integrity but that alsofacilitates a controlled and uniform removal of gaseous thermaldecomposition products from the brown part body without deforming it. Asecond component may be a non-extractable, later pyrolysed second stagebinder, which may be a thermoplastic polymer selected from variousgrades of polyethylene (PE), such as LDPE, HDPE, LLMWPE, etc.,polypropylene, poly(methyl pentene) or other nonpolar hydrocarbonpolymer. A third component may be a minor fraction of a powderdispersing component, such as long-chain saturated fatty acids (forexample, stearic (SA) or palmitic (PA) acid) that act as disaggregatingsurface active agents for the inorganic or metal powder, alternatively apolar and tacky copoly(ethylene-vinyl acetate) (PEVA) in place of afatty acid as the powder dispersing component.

In these examples, binder compositions may contain a first stage binderof 50-70 vol.-% of hydrocarbon solvent-soluble wax or fatty acidcomponents. In order to be more flexible or pliable in room temperatureor shipping conditions, the first stage binder may include low-meltingbinder components, such as higher alkanes, petrolatum, paraffin waxesand fatty acid esters and other compatible liquid plasticizers toincrease the flexibility of the polymeric binder system. Thesecomponents may improve spool winding on small-diameter spools and toresist impact during handling and shipping (including in colder ambienttemperatures, e.g., below freezing), and may also increase the rate ofextraction during the solvent debinding step.

In one particular example, a measurably volatile plasticizing bindercomponent may have relatively volatility under ambient storage, e.g.,such as naphthalene, 2-methylnaphthalene or another hydrocarbon having atriple point temperature in the vicinity of room temperature as acomponent of a primarily polyolefin binder, or as the majority componentor entire component of a first stage binder. Due to its aromaticity andlow polarity, naphthalene is compatible with a polyethylene (polyolefin)melt and has naphthalene has a relatively very low temperature triplepoint and thus very high vapor pressure over the solid phase up to themelting point at 80 degrees C. In another example, a polyolefin binderis blended with a straight- or branched chain higher (10<n<26) alkane ora mixture of such alkanes, with or without a fraction of naphthalene, inwhich the alkanes or their mixture is selected from compounds having ameasurable vapor pressure at temperatures below the melting point of thepolyolefin or below the dissolution temperature of said polyolefin inthe alkane or its mixture. “Measurable vapor pressure” means a saturatedvapor pressure higher than 0.1 Pa (1 μm Hg) at 20 degrees C.)

The alkane or its mixtures may be replaced in entirety or in part bymono-, di- or triesters of fatty acids and fatty alcohols, glycols orglycerol which also possess a measurable vapor pressure in the rangefrom ambient temperature to the dissolution temperature of thepolyolefin binder in the ester or its mixture. If the alkane, ester orits blend or a blend with a medium-size fatty acid has a measurablevapor pressure at ambient or higher temperature, but below the meltingor dissolution point of the polymer binder, it can conveniently beremoved from the blend by simply exposing the green part to low pressureenvironment, preferable at an elevated temperature, but at leastinitially at a temperature lower than the melting or dissolutiontemperature of the polyolefin binder. The sublimation or evaporation ofthe binder component will generate microporosity in the binder phase ofthe green part, thus facilitating subsequent thermal debinding of thegreen part and preventing its dimensional distortion due to theexpansion of the trapped gaseous decomposition products.

The volatile binder component should have a vapor pressure at ambienttemperature low enough so as not to vaporize to a significant degreeduring normal handling and use of the material in the open atmosphere.Volatile binder loss during long-term storage may be effectivelyprevented by storing the pellets, extruded filament or the like insealed gas- and organic vapor-impermeable multilayer packaging.Polyolefin binders include polyethylene, polypropylene or theircopolymers, as described with a wax component including a proportion ofnaphthalene, 2-methylnaphthalene. Sublimation of naphthalene duringstorage can be prevented by using an appropriate vapor impermeablepackaging material such as an aluminum-polymer laminate, yet naphthalenecan be relatively rapidly removed from the green part by moderateheating under low pressure, for example, in a vacuum oven attemperatures below the melting point of naphthalene and thus remove itwithout melting the binder phase.

As noted, in the case of FIGS. 4-40 inclusive, green body supports areprimarily for supporting the green body vs. printing forces and gravityduring the printing process, and may be removed prior to debindingand/or sintering, while the sintering supports are primarily forsupporting the brown body vs. gravity and for interconnecting supportsto the brown body for uniform shrinking, and are retained through thedebinding process and during the sintering process. The separationmaterial may be debound, and may aid in removal of the sinteringsupports after sintering. In the case of FIG. 6, the green body supportsand separation material may be combined, and the separation material andgreen body supports removed during debinding (some of the powder in theseparation material may remain), while the sintering supports are againretained for supporting the brown body vs. gravity. If it is unnecessaryto support the brown body vs. gravity (e.g., because of buoyancy effectsduring fully submerged sintering in a fluidized bed, or because ofresistance provided by powder underneath, as disclosed herein), then itthe sintering supports may be smaller, not as strong, or evenunnecessary. In this last case, this may be represented by the printingstage of FIGS. 23A and 23B, in which only green body supports/separationmaterial, but not sintering supports, are printed supporting the part.

As shown in FIGS. 23A and 23B, a powder bed or fluidized bed brown partsintering oven and process may be used together with the 3D printersdisclosed herein. The sintering oven shown in FIG. 23A, may be usedtogether with the 3D printers and debinding stations disclosed herein,those in which green body supports and separation layers are formed fromdifferent material, those in which green body supports and separationlayers are formed from the same material, and those in which nosintering supports are formed.

As shown in FIG. 23A, a sintering oven and method may support fluidizedbed sintering of the model material or composite. The release layerincludes a spherized or powder metal part, initially a brown part,during sintering to prevent warping and distortion during the sinteringprocess. For example, the part 23-3 may be placed into a crucible 23-1as shown in FIGS. 23A and 23B. The crucible 23-1 may be partially filledwith a fine powder 23-4 with size from 0.001 microns to 200 microns,preferably with size 1-20 microns. Alternatively, or in addition, if thepowder bed is to be optionally fluidized, the crucible 23-1 may bepartially filled with a powder of Geldart Group A. Geldart Group Apowders are typically substantially between 20 and 100 μm, may bespherical or irregular, and the particle density is optionally less than1.4 g/cm³. However, Geldart Group A powders are defined by bubblingbehavior, not by powder size, and any Geldart Group A powder issuitable. In a Geldart Group A powder, prior to the initiation of abubbling bed phase, beds may expand at incipient fluidization, due todecreased bulk density. Alternatively, a Geldart Group C, or Group B,powder may in some cases be suitable with mechanical or other agitation.

If the powder bed is to be fluidized, pressurized gas appropriate forsintering (e.g., typically an inert gas, or a reducing gas) may enterthe fluidized bed vessel through numerous holes via a distributor plate23-9 or a sparger distributor, the resultant gas-particle fluid beinglighter than air and flowing upward through the bed, causing the solidparticles to be suspended. Heat is applied to the crucible 23-1containing the powder bed (optionally fluidized) and part 23-3. Any partof the system may be appropriately pre-heated, e.g., a pressurized gas23-2 may be pre-heated to a temperature in the below, in the range of,or above the sintering temperature. As the part 23-3 is heated up tosintering temperature, the tendency is to deform downward under gravity,i.e., under the weight of the part 23-3 itself. In the system of FIGS.23A and 23B, the fine powder (preferably alumina, or the like) providesresistance to slumping and sagging, or in other cases, the fluidized bedof fine powder provides either or both of resistance or buoyancy. Thesystem may alternate between fluidized state and a non-fluidized state,and/or the flow rate of the fluid (gas) can further be modulated toachieve varying degrees of powder mobility. As shown, the powder in thebed continually resists weights of unsupported portions of the brownpart (e.g., unsupported portions 23-12).

Optionally, in order to promote flow, and prevent entrapment of powderin orifices and compartments of the part, the powder may besubstantially spherically shaped. Further, the powder bed can befluidized to reduce viscosity through fluid inlet and/or distributorplate 23-9. Further optionally, the crucible 23-1 is positioned in asubstantially gas-tight chamber 23-7 that seals the furnace to preventthe ingress of oxygen—which is usually detrimental to the physicalproperties of metallic powders during the sintering process. Arefractory lining 23-5 is shown, which isolates the high-temperaturecrucible 23-1 from the (preferably stainless steel) walls of thefurnace.

Further optionally, a crucible lid 23-6 may rests on top of the crucible23-1 further limiting oxygen flow into the part 23-3. As the gas flowsinto the crucible 23-1, the pressure may slightly elevate the 23-1 lidto enable gas to escape. The resulting positive pressure flowing gasseal may reduce oxygen ingress, resulting in a more pure atmospherearound the part 23-3. Further optionally, in one embodiment, thefluidizing gas may be maintained at a flow rate below a point ofmobility of the powder during an initial temperature ramp, and throughthe onset of necking among metal powder spheres in the process ofsintering—the initial stages of the sintering process. When sufficientnecking is achieved to connect many spheres and thereby maintain thestructure of the part, the gas flow can be increased to the point offluidizing the powder. Fluidizing (e.g., creating a fluidized bed)during the initial ramp (before necking) may have a destabilizing effecton the part, and may increase the likelihood of cracking or damage.However, once sintering or pre-sintering has enabled sufficient partstrength (e.g., 0.1-10% part shrinkage), and before the part hascontracted to fully sintered (e.g., 12-24%, or approximately 20%shrinkage) fluid flow may be increased to fluidize the support powderwithout damaging the part. Increasing fluid flow later in the processmay require low viscosity powder to ensure egress of powder from holes,cavities and the like.

Further optionally, the properties of the powder, fluid flow, andprinting (including part, supports, and auxiliary structures) may beconfigured to generate buoyancy of the part, on a scale from lowbuoyancy to neutral buoyancy in the fluidized bath. This effectivelyzero gravity sintering process may permit complex shapes with internalspans and bridges to be sintered without sagging or slumping. A mildamount of buoyancy will reduce the effective weight of the part or aportion of the part. However, the buoyancy may be up to neutral (thepart tends to float within the fluidized bed) or above neutral (the parttends to float to the top of the fluidized bed). A supporting hanger23-10 may counteract negative, neutral, or positive buoyancy and holdthe part immersed in the fluidized bed. In addition, a hood guard 23-11shaped to exclude powder directly above the contour of the part mayreduce or eliminate the weight of a hood or stagnant cap ofnon-fluidized powder that may reside above the part. This hood orstagnant cap may reduce overall buoyancy or buoyancy in particularlocations (see, e.g.,https://rucore.libraries.rutgers.edu/rutgers-lib/26379/). The hood guard23-11 may be 3D printed along with the part—e.g., the hood guard 23-11may be determined according to the cross-sectional shape of arepresentative or maximum horizontal section of the part, projectedupward for the expected depth of submersion in the fluidized bed. Thehood guard 23-11 may then be 3D printed as a hollow or substantiallyhollow prism or shell from model material (or sintering supportmaterial), e.g., above the part with a separation layer, or a separateprint job (subsequent or beside the part to be sintered). The hood guard23-11 may also serve the role of a supporting hanger 23-10, and the partmay be suspended via the hood guard 23-11. The hood guard 23-11 may be“sacrificial”, e.g., generated during printing but disposed of orrecycled following sintering.

Further optionally, a gas outlet 8 may allow the exhaust of thesintering process to be removed from the oven. Alternatively, or inaddition, the outlet 8 may be used to pull a vacuum on the furnace(e.g., use a vacuum pump to lower the ambient pressure toward vacuum) toremove a significant portion of the oxygen from the environment prior toflowing the inert or reducing gas for sintering and/or fluidizing thebed. Flowing gas through the powder agitates the powder in addition tofluidizing the powder. Further optionally, a fluidized bed may allow thepart to contract or shrink during sintering without the powder exertingany resistance. While the necessary gas flow to enter a particulateregime and bubbling regime in fluidizing a particular particle size andtype can be well characterized empirically or via modeling, mechanicalagitation, including by stirring members, shaking members or chambers,ultrasonic, magnetic, inductive, or the like may reduce the gas velocityneeded or provide fluidization in more inaccessible sections of thepart.

FIG. 23B shows one overall schematic of the process. Initially, in the3D printing phase, STG-1A the part 14, together with at least its greenbody supports is printed in a 3D printer as described. The green body,including all of these, optionally still bound to a higher meltingtemperature material—ceramic or other material build plate 16, may betransferred to a debinding chamber (optionally, the debinding chamber isintegrated in the 3D printer or vice versa). As noted, green bodysupports may be removed during debinding. Accordingly, as shown in FIG.24, debinding STG-2A debinds the model material, leaving a porous brownbody structure (“DEBINDING”), and may optionally include dissolving,melting, and/or catalyzing away the green body supports (“SUPPORTREMOVAL”). As discussed, sintering supports may remain even with thepowder bed or fluidized powder bed technique, but may be, e.g., placedin fewer locations or support only longer spans.

Continuing with FIG. 23B, as shown, a brown body is transferred to asintering chamber or oven (optionally combined with the printer and/ordebinding chamber). The sintering chamber or oven is filled with apowder, as described, that will not sinter at the sintering temperatureof the brown body (e.g., alumina powder surrounding n aluminum or steelbrown body to be sintered. During sintering STG-3A, the brown bodyuniformly shrinks by approximately 20%, closing internal porousstructures in the brown body by atomic diffusion. The alumina powder beddoes not sinter, but either resists sag and slumping of spans andoverhangs, and/or provides buoyancy for spans and overhangs. If thepowder bed is fluidized, the powder and part may be more uniformlyheated by the circulation of fluidizing with a gas. As shown in FIG. 24,a sintered body can be removed from the sintering oven. Some aluminapowder may remain in internal cavities and can be washed away STG-4Aand/or recovered.

With respect to sintering ovens, unlike solid metals (which may beopaque to or reflect microwaves at low temperatures), powdered metal mayadvantageously absorb microwaves. In addition, the resulting heatingprocess may be volumetric or partially volumetric, and heat a body ofpowdered material evenly throughout, including to sintering temperatures(if a compatible chamber and atmosphere can be practically provided).Furthermore, as discussed herein, smaller powder sizes (e.g., lower than10 micron, average or >90% count) may lower sintering temperatures toenable using lower temperature furnace and refractory materials. A soakin a forming or reducing gas (e.g., Hydrogen mixtures) may also be used.

A fused silica tube used for sintering (in combination with microwavesor otherwise) may be formed from very pure silica (e.g., 99.9% SiO2),and a crucible for holding the workpiece or part may be made from asimilar material. In some cases, the optical transparency of fusedsilica may correlate to its microwave transparency and/or itscoefficient of thermal expansion. A more optically transparent fusedsilica may have a lower degree of crystallization, and the crystalstructures may scatter both light and RF.

Typical Thermal Expansion Coefficients and Microwave Penetration Depths

Microwave Microwave power field Thermal penetration penetrationExpansion depth* depth* Coefficient (for 2.45 GHz) (for 2.45 GHz)Material × 10⁻⁶/° C. D, in cm d, in cm Fused Silica 0.55 3900 7800(amorphous, synthetic) Cordierite 0.1 Silicon Carbide 3.7 1 2 Mullite(can be 5.0 500 1000 damaged by H2) Alumina 7.2 625 1250 Zirconia 10.5Quartz Mineral 7-14 (natural, crystalline) Bulk, solid aluminum (1.67 ×10⁻⁶ micrometers) *Penetration depth (d) is the distance from thesurface of the material at which the field strength reduces to 1/e(approximately 0.368) of its value at the surface. The measurements inthis table are taken at or around 20 degrees C. As temperatureincreases, the penetration depth tends to decrease (e.g., at 1200degrees C., the penetration depth may be 50-75% of that at 20 degreeC.).

With respect to gas handling, different sintering atmospheres areappropriate for different metals (e.g., Hydrogen, Nitrogen, Argon,Carbon Monoxide, vacuum, reducing gases with small percentages ofHydrogen), and for different stages of a sintering process. Thesintering atmosphere may help in different stages, e.g., in completingdebinding, in cleaning away debinding remnant materials to avoidcontamination in a sintering furnace, in reducing surface oxidation, inpreventing internal oxidation, and/or to prevent decarburization. Anatmosphere controlled furnace may be used before sintering as well, ordifferent stages arranged in a muffle staged continuous furnace.

An atmosphere after initial debinding to clean away lubricants orremnant binder, but before sintering may be oxidizing (nitrogensaturated with water or with added air) through water to hightemperature metal for example, optionally deposited with a similar(primary) matrix or binder component to the model material. Aftersintering, the release layer may become highly saturated, or by use ofair additions. Temperatures may be 200-750 C with dew point of 0 to 25C. An atmosphere in sintering, especially for stainless steels or sometool steels, may be highly reducing, e.g., pure Hydrogen, with dew pointof −20 to −40 C. Nitrogen/hydrogen mixtures (3-40%) or Nitrogen/ammoniamay be used, and hydrocarbons may add back surface carbon or prevent itsloss. Atmospheres in post-sintering may be cooling (at very low Oxygenlevels, e.g., 10-50 ppm) at a rate of, e.g., 1-2 degrees C. per second,and/or may be recarbonizing with a hydrocarbon-including atmosphere(forming some CO) at e.g., 700-1000° C. range for steels.

With respect to a microwave assisted sintering furnace 113, as shown inFIG. 25, one candidate microwave generator 113-1 for assisting orperforming sintering may generate 2.45 GHz frequency microwaves at apower output of 1-10 kW. The generator, oscillator or magnetron 113-1may be connected to a waveguide 113-2 with an open exit. A circulator113-3 and dummy load 113-4 (e.g., water) may absorb reflected waves toavoid returning these to the magnetron 113-1 and redirect travelingwaves to the furnace 113 (as monitored by appropriate sensors) andadjusted. A tuner device (in addition to or in alternative to thecirculator) 113-3 may change the phase and magnitude of microwavereflection to, e.g., cancel or counter reflected waves.

As shown in FIG. 25, one technique and material variation method mayinvolve supplying a material (pellet extruded, filament extruded, jettedor cured) containing a removable binder as discussed herein (two or onestage) and greater than 50% volume fraction of a powdered metal having amelting point greater than 1200 degrees C. (including various steels,such as stainless steels or tool steels). The powdered metal may havewhich more than 50 percent of powder particles of a diameter less than10 microns, and advantageously more than 90 percent of powder particlesof a diameter less than 8 microns. The average particle size may be 3-6microns diameter, and the substantial maximum (e.g., more than the spanof +/−3 standard deviations or 99.7 percent) of 6-10 microns diameter.The particle size distribution may be bimodal, with one mode atapproximately 8 micron diameter (e.g., 6-10) microns and a second modeat a sub-micron diameter (e.g., 0.5 microns). The smaller particles inthe second mode assist in early or lower temperature necking to preservestructural integrity.

Smaller, e.g., 90 percent of less than 8 microns, particle sizes maylower the sintering temperature as a result of various effects includingincreased surface area and surface contact among particles. In somecases, especially for stainless and tool steel, this may result in thesintering temperature being within the operating range of a fused tubefurnace using a tube of amorphous silica, e.g., below 1200 degrees C.Accordingly, in the process variation, as discussed herein, this smallerdiameter powder material may be additively deposited in successivelayers to form a green body as discussed herein, and the binder removedto form a brown body (in any example of deposition and/or debindingdiscussed herein).

As shown in FIGS. 24 and 25, the brown part may be loaded into the fusedtube furnace (furnace 113 is one example) having a fused tube 113-5formed from a material having an operating temperature less thansubstantially 1200 degrees C., a thermal expansion coefficient lowerthan 1×10⁻⁶/° C. and a microwave field penetration depth of 10 m orhigher (e.g., amorphous fused silica having an operating temperaturepractically limited to about 1200 degrees C., a thermal expansioncoefficient of about 0.55×10⁻⁶/° C. and a microwave field penetrationdepth of more than 20 m). The low thermal expansion coefficient relatesto the ability to resist thermal shock and therefore to ramp temperaturequickly and handle high thermal gradients in operation and in furnaceconstruction. For example, using a thermal shock resistant material maypermit ramping a temperature inside the fused tube at greater than 10degrees C. per minute but less than 40 degrees C. per minute. Themicrowave field penetration depth relates to microwavetransparency—higher penetration depths are related to highertransparency.

As shown in FIGS. 24 and 25, in this process the fused tube 113-5 may besealed by a fused silica plug or plate 113-6 (and/or a refractory orinsulating plug or plate). The internal air may be evacuated, and may befurther replacing internal air with a sintering atmosphere (includingvacuum, inert gas, reducing gas, mixtures of inert and reducing gas).Microwave energy may be applied from the microwave generator 113-1outside the sealed fused tube to the brown part. In this case, becausethe small particles may lower the sintering temperature, the brown partof steel may be sintered in this furnace at a temperature lower than1200 degrees C. In one advantageous example, more than 90 percent of theprinting material's powder particles have a diameter less than 8microns. Some of these particles, or particles in the remaining 10%, mayhave a diameter less than 1 micron (e.g., >90% of these having adiameter less than 0.5 microns).

As shown in FIGS. 24 and 25, because microwaves may be difficult todirect for evenly distributed heating (e.g., even with the use ofturntables and reflective stirring blades), the system may use susceptormembers 113-7 (e.g., rods distributed about the perimeter). Thesusceptor members 113-7 may be made from a microwave absorbing materialthat resists high temperatures, e.g., silicon carbide. The susceptormembers 113-7 may be passive (energized only by microwave radiation),active (resistively heated), or a mixture of the two. The susceptormembers 113-7 discussed herein may even be used without microwaveheating (in a microwave-free system, silicon carbide and MoSi₂, twocommon susceptor materials, are often also good resistive heaters forhigh temperatures). Further as shown in FIGS. 24 and 25, the microwaveenergy is applied from outside the sealed fused tube 113-5 to susceptormaterial members 113-7 arranged outside the sealed fused tube (whichdoes not contaminate the sintering atmosphere in the tube interior). Asnoted, the sintering atmosphere is appropriate for the powdered metalbeing sintered, e.g., inert, vacuum, or at least 3% Hydrogen (e.g., 1-5%hydrogen, but including up to pure hydrogen) for stainless steels.

In a variation approach for producing finely detailed parts, again thematerial having a removable binder and greater than 50% volume of apowdered steel (or other metal) is supplied with more than 50 percent ofthe powder particles have a diameter less than 10 microns,advantageously more than 90 percent having a diameter equal to or lessthan substantially 8 microns. The material may be additively depositedwith a nozzle having an internal diameter smaller than 300 microns,which provides fine detail but is 10-20 times the diameter of the largerparticles of the powder (preventing jamming). Again, the binder isremoved to form a brown body and the brown part loaded into the fusedtube, e.g., amorphous silica, having a thermal expansion coefficientlower than 1×10-6/° C., and the is sealed and the atmosphere thereinreplaced with a sintering atmosphere. Radiant energy (e.g., radiant heatfrom passive or active susceptor rods or other resistive elements,and/or microwave energy) is applied from outside the sealed fused tube113-5 to the brown part, sintering the brown part at a temperaturehigher than 500 degrees C. but less than 1200 degrees C. (a rangeenabling small particle aluminum as well as small particle steelpowders). In this case, the nozzle may be arranged to deposit materialat a layer height substantially ⅔ or more of the nozzle width (e.g.,more than substantially 200 microns for a 300 micron nozzle, or 100microns for a 150 micron nozzle).

In another variation suitable for sintering both aluminum and stainlesssteels (in addition to possible other materials) in one sinteringfurnace 113, parts formed from either small particle powder may beplaced in the same furnace and the atmosphere and temperature rampingcontrolled substantially according to the material. For example, a firstbrown part may be formed from a first debound material (e.g., aluminumpowder printing material) including a first powdered metal (e.g.,aluminum), in which more than 50 percent of powder particles of thefirst powdered metal have a diameter less than 10 microns, and a secondbrown part formed from a second debound material (e.g., stainless steelpowder printing material) including a second powdered metal (e.g.,stainless steel) in which more than 50 percent of powder particles ofthe second powdered metal have a diameter less than 10 microns. In afirst mode for the furnace, the aluminum brown part may be loaded intothe amorphous silica fused tube discussed herein, and the temperatureramped at greater than 10 degrees C. per minute but less than 40 Cdegrees C. per minute to a first sintering temperature higher than 500degrees C. and less than 700 degrees C. In a second mode, the stainlesssteel brown part may be loaded into the same fused tube, and thetemperature inside the fused tube ramped (e.g., by the heat control HCand or microwave generator MG) at greater than 10 degrees C. per minutebut less than 40 degrees C. per minute to a second sintering temperingtemperature higher than 1000 degrees C. but less than 1200 degrees C.

The atmosphere may be changed by the pressure control 113-8 and/or flowcontrol 113-9, operating the vacuum pump 113-10 or gas source 113-11. Inthe first mode for aluminum, a first sintering atmosphere may beintroduced into the fused tube 113-5, including inert Nitrogen being99.999% or higher free of Oxygen. In the second mode for stainlesssteel, a second sintering atmosphere comprising at least 3% Hydrogen maybe introduced.

As shown in FIG. 25, in the multipurpose sintering furnace suitable forrapidly sintering both aluminum and stainless steel at below 1200 C,using small diameter powders as discussed herein, the furnace mayinclude a fused tube 113-5 formed from a fused silica having a thermalexpansion coefficient lower than 1×10-6/° C. (a loose powder, permittinghigh ramp rates, the tube being resistant to thermal shock), and a sealthat seals the fused tube versus ambient atmosphere. A tube-internalatmosphere regulator (e.g., including the high vacuum 113-10 pump orother device, the pressure control 113-8, the flow control 113-9, and/orthe gas source(s) 113-11) maybe operatively connected to an interior ofthe fused tube 113-5 to apply vacuum to remove gases (including air andwater vapor) within the fused tube 113-5 and to introduce a plurality ofsintering atmospheres (including vacuum, inert, and reducing atmospheresin particular) into the fused tube. Heating elements (e.g., theresistive heater and/or susceptor 113-7 and/or the microwave generator113-1) are placed outside the fused tube 113-5 and outside any sinteringatmosphere within the fused tube 113-5 so as not to contaminate thesintering atmosphere. A controller (e.g., 113-12) may be operativelyconnected to the heating elements 113-7 and/or 113-1 and the internalatmosphere regulator. In a first mode, the controller 113-12 may sinterfirst material (aluminum) brown parts within a first sinteringatmosphere (<0.001 percent oxygen in nitrogen) at first sinteringtemperature higher than 500 degrees C. and less than 700 degrees C. In asecond mode, the controller may sinter second material (stainlesssteels) brown parts within a second sintering atmosphere (e.g., inert orreducing atmosphere) at a second sintering temperature higher than 1000degrees C. but less than 1200 degrees C. An (optical) pyrometer 113-13may be used to observe sintering behavior through the seal. The oven 113is held in an appropriate microwave reflective enclosure 113-14 and isinsulated with appropriate insulation 113-15 and refractory material113-16.

As shown in FIGS. 24 and 25, the internal atmosphere regulator may beoperatively connected to an interior of the fused tube 113-5 tointroduce the sintering atmospheres, and may ramp a temperature insidethe fused tube 113-5 at greater than 10 degrees C. per minute but lessthan 40 degrees C. per minute. This is typically not recommended withhigher thermal expansion ceramics like alumina or mullite. Also, themicrowave field penetration depth of 20 m or higher of amorphous silicapermits higher microwave penetration efficiency. The microwave generatorMG applies energy to, and raises the temperature of, the first and/orsecond material brown parts within the fused tube 113-5, and/or thesusceptors 133-7, which then re-radiate heat to heat the first and/orsecond material brown parts.

Accordingly, a small powder particle size (e.g., 90 percent of particlessmaller than 8 microns, optionally including or assisted by particles ofless than 1 micron) of metal powder embedded in additively depositedmaterial lowers a sintering temperature of stainless steels to below the1200 degree C. operating temperature ceiling of a fused silica tubefurnace, permitting the same silica fused tube furnace to be used forsintering both aluminum and stainless steel (with appropriateatmospheres), as well as the use of microwave heating, resistantheating, or passive or active susceptor heating to sinter bothmaterials.

As discussed herein, interconnected channels may be printed betweeninfill cells or honeycomb or open cells in the part interior, thatconnect to the part exterior, and a shell (including but not limited toa support shell) may have small open cell holes, large cells, or ahoneycomb interior throughout to lower weight, save material, andimprove penetration or diffusion of gases or liquids (e.g., fluids) fordebinding. These access channels, open cells, and other debindingacceleration structures may be printed in the part or supports(including shrinking/densification supports or shrinking/densificationplatform). All or some of the channels/holes may be sized to remain openduring debinding (including but not limited to under vacuum), yet closeduring the approximately 20% size reduction of sintering. Internalvolumes may be printed with a channel to the outside of the part topermit support material to be removed, cleaned away, or more readilyaccessed by heat transfer or fluids or gasses used as solvents orcatalysis.

Debinding times for debinding techniques involving solvent or catalystfluids (liquid, gas, or other) may be considered in some cases to dependon the part “thickness”. For example, a 4 cm thick or 2 cm thick partmay debind more slowly than a 1 cm thick part, and in some cases thisrelationship is heuristically defined by a debinding time of, e.g., somenumber of minutes per millimeter of thickness. The time for removingdebinding fluid (e.g., drying or cleaning) may also increasesubstantially proportionately with thickness. According to the presentembodiment, the effective thickness of a part for the purposes ofdebinding time may be reduced by providing the aforementioned fluidaccess to an interior of the part, using channels from the exteriorwhich may either remain open through sintering or be (effectively)closed following sintering.

Such channels may include at least one access channel to an exterior ofthe part, e.g., penetrating from the exterior of the part through wallstructures of the 3D printed shape to one, several, or many infillcavities of the part; or may alternatively be surrounded by wallstructures of the part. In some cases, an interconnected channel mayinclude at least two access channels to an exterior of the part thatsimilarly penetrate a wall, in order to provide an inlet and an outletfor fluid flow or simply to permit fluid to enter versus surface tensionand/or internal gas. These inlet-honeycomb-outlet structures may bemultiplied or interconnected. In some cases, the inlets may be connectedto pressurized fluid flow (e.g., via either 3D printed or mechanicallyinserted flow channel structures). In some cases, the inlets may beconnected to vacuum or a flushing gas. In some cases, “inlet” and“outlet” are interchangeable, depending on the stage of the process.

For example, the 3D printer according to FIGS. 1A-40 inclusive may beemployed to feed the composite material including the binder matrix anda sinterable powder. “Walls” in a layer or shell follow positivecontours or negative contours of a 3D model and are positioned accordingto the mesh or model outline or surface, and may be one or more roads orlayers or shells thick (adjacent walls formed by offsetting from themodel outline or surface). Internal walls (including horizontal walls as“roofs” or “floors”) may also be formed, typically connecting to orextending from walls that follow the outer or inner contour of the 3Dmodel shape. “Infill” or honeycomb extends between and among walls,floors, and roofs. The 3D printer may deposit a wall or successivelayers of a wall, the wall having an access channel extending from anexterior of the part to an interior of the part. The access channelpermits fluid to enter the interior (e.g., between positive and negativecontours of a cross-section of the part). As shown, e.g., in FIGS.26A-31, it is not necessary that the entirety of the interior of a partbe interconnected to reduce the debinding time. For example, awall-penetrating access channel and interconnected honeycomb (e.g., viaa distribution channel) may be connected to route fluid to a locationwithin a specified distance of the deepest interior region of a part; orto set a specified distance of a wall or walls of the part to a nearestfluid-filled chamber.

The 3D printer may deposit successive layers of honeycomb infill withinthe interior (e.g., between walls tracing positive and negative contoursof the part), and the honeycomb infill may have a distribution channel(or several, or many distribution channels) connecting an interiorvolume of the honeycomb infill to the access channel. The 3D printer orsubsequent debinding station or part washer may debind the binder matrixby flowing a debinding fluid through the access channel and/ordistribution channel(s) and within the interior volume of the honeycombinfill.

FIG. 26A and FIG. 26B substantially correspond to FIGS. 5B and 5D,respectively, and show selected sections through FIG. 4 for the purposeof discussing printing and other process steps. As shown in FIGS. 4 and26A, following the printing of the raft separation layer SL1, a raft RA1of model material (e.g., metal-bearing composite) is printed. The raftor shrinking platform or densification linking platform RA1 may includerouting channels CH1 therethrough for connecting to or directing fluidto access channels of the part. There may be one, several, or as shown,an array of routing channels CH1. The routing channels CH1 may connectduring debinding to a matching one, several or array of debinding fluidsupply channels (e.g., as shown in FIG. 25). Alternatively, or inaddition, fluid flow through the routing channels may be promoted viacirculation, heating, or agitation in an immersed bath of debindingfluid. Agitation may be forced fluid, mechanical, inductive, magnetic,or the like. The raft or shrinking platform RA1 is otherwise similar tothat discussed with reference to FIG. 5B.

As shown in FIGS. 4 and 26B, the surrounding shell support structure SH1is continued printing in layers, and the internal volume V1 as well asthe part interior may be printed with a channel (e.g., distributionchannels CH3 leading to access channels CH2, not shown) to the outsideof the part to permit support material to be removed, cleaned away, ormore readily accessed by heat transfer or fluids or gasses used assolvents or catalysis. In the case of FIGS. 4, 26A, and 26B (and otherFigures as well), as noted, solid bodies are shown to simplifyexplanation, but the internal structure of the solid bodies may be 3Dprinted with infill patterns (e.g., honeycombs) and/or may includechopped, short, long, or continuous fiber reinforcement. Two examplesare shown in FIG. 26C and FIG. 26D.

As shown in FIG. 26C and FIG. 26D, respectively, hexagonal andtriangular honeycombs (which, shown in cross section, may include bothcavities and infill formed in a vertical prism, columnar, or may beoffset polyhedral cavities/infill) is employed as infill. Twodistribution channels CH3 are shown in each sectioned layer. Thedistribution channels CH3 may be distributed about many layers (e.g.,may be formed among a few layers) to interconnect some, many, or allinfill or honeycomb cells. FIG. 26C also shows an access channel CH2,which may interconnect with the distribution channels CH3 by channel andcell cavity paths spanning different layers of the deposition. Thechannels CH2 and CH3 are angled through infill and walls of the part,which can increase the length of a channel and/or decrease the number ordegree of turns in the fluid flow. In this manner—by changing the lengthor straightness of channels CH2 or CH3—fluid flow throughout thechannels CH2 and CH3 part can be balanced for evenness orincrease/decreased flow in a particular region.

FIG. 27 shows a side sectional view, substantially similar indescription to FIGS. 4, 6, 8 and 9, in which the honeycombcavities/infill are formed as vertical, columnar prism shapes.Distribution channels CH3 (e.g., approximately 20 shown) are shown amongthe many layers of the deposited part. The distribution channels CH3 areshown distributed about many layers to interconnect some, many, or allinfill or honeycomb cells. No channels extend into overhangs OH2 or OH4,which may not be thick enough to need additional debinder fluid flow. Asshown, sintering support or form-fitting shell SH3 may also be filledwith infill cells, and may or may not additionally include channels,access or distribution channels CH2 or CH3 (none shown in FIG. 27). FIG.27 does not show the optional access channel CH2, in the case where thedistribution channels CH3 by themselves increase debinding speed. In onevariation, 20% or fewer of the vertical honeycomb cavities of theinfill, or vertical column cavities having an area of less than 5% ofthe area of a largest cross section, act as distribution channels.

FIGS. 27 and 28 show a side sectional view, substantially similar indescription to FIGS. 4, 6, 8 and 9 (common reference numbers beingsimilarly described), in which the honeycomb cavities/infill are formedas vertical, columnar prism shapes. Distribution channels CH3 (e.g.,approximately 20 shown) are shown among the many layers of the depositedpart. The distribution channels CH3 are shown distributed about manylayers to interconnect some, many, or all infill or honeycomb cells. Nochannels are shown extending into overhangs OH2 or OH4, which may not bethick enough to need additional debinder fluid flow. As shown, sinteringsupport or form-fitting shell SH3 may also be filled with infill cells,and may or may not additionally include channels access or distributionchannels CH2 or CH3 (none shown in FIG. 27). FIG. 27 does not show theoptional access channel CH2, i.e., showing the case where thedistribution channels CH3 by themselves increase debinding speed.However, the access channels CH2 shown in other Figures and describedherein may be applied to the structure of FIG. 27. FIG. 28 shows accesschannels CH2 which provide ingress and egress for fluid flow into thedistribution channel CH3 interconnected honeycomb cells. As should benoted throughout, dimensions for channels may be exaggerated, and breaksin walls as shown merely through holes—the distribution channels CH3 maybe small circular holes, and take up less than 1% (e.g., less than 1-3%)of the surface area of the infill, and similarly, the access channelsCH2 may be small circular through holes which take up less than 1%(e.g., less than 1-3%) of the surface area of the part walls.

FIG. 29 shows a side sectional view, substantially similar indescription to FIGS. 4, 6, 8, 9, 27, and 28 (common reference numbersbeing similarly described) in which the distribution channelscavities/infill are formed in an aligned, and/or angled, mannerthroughout the columnar prism shapes. As discussed, changing thediameter, length and/or straightness of the channels CH3, or depositingobstacles or baffles within them, may increase or decrease resistance toflow. In contrast to FIG. 28, the sintering support or shell structuresSH3 and SH4 also include access channels CH2 to permit fluid flowtherethrough (both an inlet and outlet). Further, routing channels CH1are printed in intervening layers (e.g., raft RA2, shell structures SH3,SH4, release or separation layers SL3), and in this case may match amatching routing channel provided in the print bed or build plate (e.g.,to provide fluid flow access in those cases where a print bed or buildplate may be transported together with the green and/or brown partthroughout the debinding and/or sintering process).

FIG. 30 shows a side sectional view, substantially similar indescription to FIGS. 4, 6, 8, 9, 27, 28 and 29 (common reference numbersbeing similarly described) in which the distribution channels CH3throughout cavities/infill are formed in an aligned, and/or angled,manner throughout cellular (octahedral as one example) polyhedronstacked shapes, and in which access channels CH2 are provided in threelocations in this section. It should be noted that wall thicknesses maybe maintained substantially constant (e.g., within 5% of thickness)throughout—e.g., the exterior wall or shell thickness of the part beingthe same as the interior walls of the infill, and/or either being thesame as walls forming distribution or access channels, and/or any ofthese being the same thickness as walls forming the sintering supportstructures or shrinking platform.

FIG. 31 shows a side sectional view, a closer view of the exemplary partof the process diagram of FIG. 25, substantially similar in descriptionto FIGS. 4, 6, 8, 9, 27, 28 29, and 30 (common reference numbers beingsimilarly described), in which the distribution channels CH3 throughoutcavities/infill are formed in an aligned, and/or angled, mannerthroughout cellular prism shapes, and in which access channels CH2 areprovided in two locations in this section. The distribution channelspass near to, adjacent to, or proximate to the portion of the partinterior farthest from, deepest within, or thickest TH with reference toa negative or positive contour or wall of the part. As discussed withreference to FIG. 25, the uppermost region of the part shown in FIG. 31does not include channels, as the part interior is close enough todebinder fluid flow such that it may be expected that the uppermostregion of the part may debind in an acceptable time.

Accordingly, as shown in FIGS. 25-31, the process of forming a “thick”part amenable to rapid fluid-based debinding may include depositingsuccessive layers of the wall of the part to form not just one accesschannel CH2, but also a second access channel CH2 extending from theexterior of the part to the interior of the part. This may assist indebinding the binder matrix by flowing a debinding fluid in through thefirst access channel, via the distribution channel, and out through thesecond access channel. In this case, the first access channel CH2 may beconnected to a pressurized supply of debinding fluid to force debindingfluid through and/or throughout the first access channel, distributionchannel(s), and second access channel. Additionally, or in thealternative, in this process, successive layers of honeycomb infill maybe deposited in the interior of the part to form a plurality ofdistribution channels CH3 connecting an interior volume of the honeycombinfill to the first access channel CH2, at least some of the pluralityof distribution channels CH3 being of different length from other of thedistribution channels CH3.

As shown in FIGS. 32 and 33A-33D, companion ceramic sintering supportsmay be printed using a ceramic composite material that behavesdimensionally similarly to the metal model material but does notchemically react with and thus doesn't sinter together with it. As apart and its companion ceramic sintering supports CSS may sinteraccording to any particular temperature profile suitable for sinteringthe part's model material, the material of the ceramic sintering supportshrinks by a particular amount and in some cases along a particulardensity profile (e.g., starting and ending density, starting and endingtemperatures, shape of the curve between) according to at least thecomposition of the ceramic sintering support material. To match thesintering behavior of the ceramic sintering supports to that of the partmodel material, as noted, the amount of final shrinkage should be thesame. As shown in FIG. 32, optionally, the amount of shrinkage of theceramic sintering support material should be more than that of the partmodel material until the final shrinkage amount is reached. Furtheroptionally, the ceramic sintering support material may begin to shrinkat a lower temperature or earlier at the same temperature.

In general, the substantial temperature ramp and environmentalconditions (such as gases) for sintering a target metal part modelmaterial is presumed to be the temperature ramp to be used, because thepart must sinter adequately with or without supports. Exceptions arepossible (e.g., minor changes to the part model sintering temperatureramp to allow the supports to function better). Under these conditions(e.g., given a temperature ramp suitable for sintering a metal partmodel material), a candidate first ceramic material, e.g., α-alumina orother alumina, having a sintering temperature above that of the partmodel material may have its sintering temperature lowered and/or itsshrinkage amount changed by (i) reducing average particle size (“APS”)or (ii) mixing in a compatible second or third lower temperaturesintering material (e.g., silica, or yttria-silica-zirconia). Thesemixed materials would also be sintered. In addition, or in thealternative, a non-sintering filler that sinters at a significantlyhigher temperature may be mixed (which will generally decrease theamount of shrinking or densification). In general, homogeneous materialshaving a smaller APS will start densifying at lower temperatures andwill attain a full density at a lower temperature than the larger APSmaterials.

In addition, or in the alternative, the sintering temperature, shrinkingamount or the degree of densification can be changed by changing theparticle size distribution (“PSD”, e.g., for the same average particlesize, a different proportion or a bimodal composition of larger andsmaller particles) or by changing the particle volume loadingpercentage. In addition, or in the alternative, when materials that mayreact are mixed, the sintering temperature, shrinking amount or thedegree of densification of the mixture can be changed by using componentmixing that may densify at a lower temperature than a chemical reaction,e.g., combining alumina and silica in a manner that densifies (sinters)at a temperature lower than that which forms mullite. For example,alumina-silica powder may be generated as alumina powder particles eachforming an alumina core with a shell of silica, where the mixture firstdensifies/sinters between, e.g., 1150 and 1300 deg C., and converts tomullite only at higher temperatures, e.g., 1300-1600 degrees C.

In addition, or in the alternative, the sintering temperature, shrinkingamount or the degree of densification can be changed by changing adegree of homogenization (molecular, nano-scale, core-shell structures)of dissimilar components. In the case of part shapes including either orboth of convex or concave shapes (protrusions, cavities, or contours),as shown in FIGS. 33A-33D, a sintering support made of a material havinga different shrinkage rate or shrinkage amount can cause either or bothof slumping or interference that can could cause the shape to deform. Itshould be noted that FIGS. 33A-33D are exaggerated in scale.

An appropriate sintering support material may have a final shrinkageamount over the same time-temperature sintering profile as the modelmaterial, as discussed herein. However, perfect matching of rate andfinal shrinkage percentage is not necessary. For example, the sinteringsupport material should not shrink at a slower rate than the modelmaterial, or concave shapes on the part may be deformed and may not berestored by gravity. However, should the sintering support materialshrink at a faster rate than the model material, printed sinteringsupports may not interfere with many concave shapes of the part (e.g.,as shown in FIG. 33B). In addition, for a faster shrinking sinteringsupport, the printed supports may be split, and gaps printed intosintering supports, to avoid interfering with and/or deforming eitherconvex shapes or certain concave shapes. In this case, gravity and someelastic behavior at sintering temperatures,—even if the sinteringsupport material shrinks at a faster rate than the model material—willpermit the part and the sintering supports to “match up” at the finalsintering shrinkage amount.

As shown in FIGS. 33C and 33D gaps may be printed side-to-side, in thevertical direction or horizontal direction, together with green bodysupports and/or a separation layer between each ceramic sinteringsupport and the part (including between adjacent ceramic sinteringsupports). Gaps may be printed adjacent convex or concave part shapes orcontours. In addition, gaps may be printed adjacent convex or concavepart shapes or contours where a surface of the part and a surface of aceramic support follow respective paths that would, without the gap,interfere during shrinking. In the case of vertical gaps, a small amount(e.g., a few mm) of unsupported span of part material is stiff enough toresists gravity-caused slump during sintering. In the case of horizontalor diagonal gaps, a separation layer in the gap including remnant powder(spheres) following debinding will permit substantially free horizontalor diagonal sliding of the ceramic support during sintering.

However, as shown in FIGS. 33A-33D, even when the ceramic sinteringsupports shrink/sinter earlier than and/or faster than and/or equal tothe metal part material until the target density, substantiallydiffering shrink rates or other differences in bulk density curve overtime (e.g. differing starting or ending positions, differing curveshapes) may require some rearranging of some sintering supportsfollowing debinding, such that the shrink rate profile of the modelmaterial to the sintering support material be matched to within 5percent of the bulk density of the model material over rising andconstant temperature portions of a sintering temperature ramp.

FIGS. 34A and 34B show a flowchart and schematic, respectively, thatshow a gravity-aided debinding process useful with parts as describedherein printed with channels CH1, CH2, and/or CH3 (or even in some caseswithout). FIGS. 34A and 34B are described and shown using thecross-sectional structure of FIG. 29 (having such channels) as anexample. As shown in FIGS. 34A and 34B, access, routing, anddistribution channels permit fluid to enter the part interior to morequickly debind the green part to a brown part. Debinding as a solventbased (including with thermal assistance, or thermal debinding withsolvent assistance) or catalytic process may take hours, sufficient timeto permit fill-purge fluid cycles. In one exemplary process, as shown inFIGS. 34A and 34B, a part with access, distribution, and/or routingchannels is placed in a debinding chamber, container or facility in stepS341. As shown in FIG. 34B, the part may be suspended or put on a porousrack or otherwise held in a manner that leaves at least top and bottomchannel inlets and outlets relatively clear of obstructions to gravitybased fluid flow.

In Step S342, the chamber may be filled with solvent or other debindingagent (alternatively, or in addition, the part is lowered or otherwiseplaced into a pre-filled bath). In Step S343 the part is kept in thedebinding agent for a predetermined, modeled, calculated, or measureddwell time. The dwell time may be sufficient for, e.g., the debindingagent to permeate the channels. The dwell time may be additionally oralternatively sufficient for, e.g., the debinding agent to debind thefirst matrix material by a first effective amount (e.g., 5-30% or higherby volume of matrix material removal). The dwell time or period in StepS343 may be enhanced by, as shown in FIG. 34B, by agitation (e.g.,mechanical members, entire chamber, bubbles, etc.), vibration and/orcirculation. In optional step S344, a property or characteristicrepresentative of the state of debinding may be detected and/ormeasured, and optionally used as a trigger to start a draining processto purge or drain debinding agent and removed material in preparationfor a next cycle (there may be only one cycle in some cases ofmeasurement). Exemplary measurements would be (i) via an optical orelectromagnetic sensor, measuring a property such as opacity, color,capacitance, inductance representative of an amount of material debound(ii) via a mechanical or fluid-responsive sensor (optionally connectedto an optical or electromagnetic element), measuring a property such asnatural frequency, viscosity, or density or (iii) via a chemical sensor(optionally connected to an optical or electromagnetic element)measuring a chemical change such as pH, oxygen content, or the like.

In step S345, and as shown in FIG. 34B, the debinding chamber may bedrained via gravity into a reservoir. Given sufficient time, andoptionally aided by agitation, heating, circulation, or otherthermomechanical processes, internal debinding agent fluid-filledchannels (such as distribution and access channels) within the part alsodrain. The reservoir may include a filter, baffles, or other cleaner forremoving debound material, and/or catalytic, chemical, magnetic,electrical or thermomechanical agent(s) for precipitating or otherwisegathering or removing debound material from the debinding agent.Alternatively, or in addition, the reservoir may include a valve foreffecting the drain from the debinding chamber, and/or a pump forrecirculating debinding agent back into the debinding chamber.Alternatively, or in addition, the reservoir may be integrated in thedebinding chamber (e.g., recirculated in the debinding chamber aftermaterial removal).

In step S346, and as shown in FIG. 34B, post draining or partialdraining, a measurement may be taken to gauge to progress of debindingand set a subsequent stage trigger or instruction for the next cycle.The sensor applicable may be similar or the same as that described withreference to step S344. In addition, or in the alternative, the partweight may be measured (before and after a debinding cycle) via a loadcell, etc. In a case where the number of cycles of filling and drainingthe chamber is relatively low (e.g., 2-10 cycles), the changing partweight may be recorded (e.g., as a profile) and used to determine thetime, temperature, and/or agitation of a subsequent cycle. In a casewhere the cycle count is 2-10 or higher (e.g., including continuousrecycling and/or fill/drain), the profile of weight change may also beemployed to model an exponential decay constant relating to the maximumremovable binder per part weight and set a termination cycle count ortime based on the exponential decay constant (e.g., terminating at atime or cycle count for 90-95% removed material by weight based on theexponential decay rate).

In step S347, and as shown in FIG. 34B, cycles may repeat until complete(“N CYCLES” being determined by predetermined count or time, by director indirect measured feedback as described above, or other modeling).When the cycles of debinding via gravity-based fill/drain cycles arecomplete, the green part has become a brown part, and may be actively orpassively dried or otherwise post-processed in preparation forsintering. As shown in FIG. 35, and noted herein, the green parts may beformed from a curable and/or debindable photopolymer including asinterable powder, as well as optionally a second stage binder (either adebindable, e.g., pyrolysing photopolymer or thermoplastic). As noted inthe CFF patent applications and other prior patent applicationsincorporated herein, different additive manufacturing processes caninclude a matrix in liquid (e.g., SLA) or powder (e.g., SLS) form tomanufacture a composite material including a matrix (e.g., debindableplastic) solidified around the core materials (e.g., metal powder). Manymethods described herein can also be applied to Selective LaserSintering which is analogous to stereolithography but uses a powderedresin for the construction medium as the matrix as compared to a liquidresin. The reinforcement might be used for structural, electricalconductivity, optical conductivity, and/or fluidic conductivityproperties. As described in the CFF patent applications and other priorpatent applications incorporated herein, and as shown in FIG. 35, astereolithography process is used to form a three-dimensional part, thelayer to be printed being covered with resin, cured with UV light or alaser of a specified wavelength, the light used to cure the resinsweeping over the surface of the part to selectively harden the resin(matrix) and bond it to the previous underlying layer.

FIG. 35 depicts an embodiment of the stereolithography process describedabove. Description of FIGS. 1A and 1B herein would be recognized by oneof skill in the art as consistent with FIG. 35 (despite differences inreference numbers). As depicted in the figure, a part 1600 is beingbuilt on a platen 1602 using stereolithography. The part 1600 isimmersed in a liquid resin material 1604 contained in a tray 1606. Theliquid resin material may be any appropriate photopolymer (e.g.,debindable composite including a primary debindable component andoptionally a secondary debindable component and a sinterable powder). Inaddition to the resin bath, during formation of the part 1600, theplaten 1602 is moved to sequentially lower positions corresponding tothe thickness of a layer after the formation of each layer to keep thepart 1600 submerged in the liquid resin material 1604. In the depictedembodiment, a laser 1612, or other appropriate type of electromagneticradiation, is directed to cure the resin. The laser may be generated bya source 1616 and is directed by a controllable mirror 1618.

Extrusion type and other deposition 3D printers employ various printingapproaches for completing perimeters, in particular for reducing seamsresulting from extruding a closed perimeter path. Any path point not ona perimeter path is in an interior region, because the perimeter pathconstitutes the outermost path points (e.g., a new path that forms partof the outer perimeter renders previous paths to be interior regions).Accordingly, printing paths may form a seam with a butt joint or otherthan a butt joint (or example, overlapping, self-crossing,interlocking). Generally, one segment and one seam is preferred becausefewer seams tend to have superior aesthetics, sealing, and dimensionalstability. Further, wall or shell contour paths (in contrast to “raster”fill paths) have been deposited in a same rotational direction—eitherclockwise or counterclockwise. Paths are printed in the same clockwiseor counterclockwise direction even if a perimeter path branches to theinterior. This simplifies and speeds printing as perimeter paths can becontinuously printed without reflex angle turns (e.g., turns of lessthan 180 degrees) from the current heading.

In the case where a printer deposits a composite feedstock intended tobe debound then sintered, and a second stage binder in place duringsintering includes retaining polymers of a common molecular lengths,deposition may create stress along the polymer molecule chains (e.g.,HDPE etc.) within at least the second stage binder aligned to someextent along the deposition paths. In the green or brown state, thestresses may not have any particular effect on dimensional stability.However, as the part is heated in the sintering process, the stressesmay relax or pull in each layer, cumulatively changing the shape of thepart if many small changes add up in the many layers of the part.

In such a case, brown parts may be dimensionally consistent with thedeposited green part, but may display a twist around a vertical axisafter sintering. In a case where heating a brown part to mild levels(e.g., 150-200 C) causes twist, the second stage polymer binder may beconsidered to be heated to a level where residual stress can relax,causing the twist, as deposition stress built into the brown part isrelaxed. As the printer deposits a layer, long chain molecules thatcompose the second stage binder polymer (the part of the binder that isleft after the primary debind) may be strained along the printingdirection. When heated to a relaxing temperature, the molecules may pullback, potentially causing a macroscopic twist in the part as pulls amongmany layers accumulate.

One countermeasure for twist is to print roads in a counteracting orretrograde direction. The three most common categories of roads areshells or walls, which are printed to form the perimeter of a slicedinterior or exterior contour; “raster” fill, which is printed to fillinterior volume in a solid manner, and infill honeycomb, which isprinted to fill interior volume in a honeycomb. In addition, interiorvolume may be filled in any coverage pattern including non-raster ornon-boustrophedon fills that cross road and/or are parallel or adjacentother roads or contours (e.g., random fill, wall-following fill, spiralfill, Zamboni-pattern fill, or the like), and may be filled in variablesize, randomized, anisotropic, foam-like, sponge-like, 3-dimensional, orother versions of regular and irregular cellular (cell walls and lowdensity or atmosphere cell interior) fills. For shells or walls, many ormost parts are not formed from vertical prism shapes and through-holes,so layer to layer the shape of a slice and the shape of the shell or allincrementally changes for different wall slopes, concavities andconvexities. Close to upper and lower surfaces, the incremental changein wall or shell shape may be more significant.

At a topmost horizontal or substantially horizontal flat layer with,e.g., protrusions or another shape beginning in the layer above, theshape of shells or walls may change completely from one layer to thenext. Accordingly, it is optionally advantageous to print first andsecond sets of opposing direction walls or shells within one layer, soas to avoid layer-to layer comparison which may be more complex. Oneapproach is to print each outer perimeter or negative contour innerperimeter with a companion, parallel, adjacent wall or shell road. Insuch a case, the length of the companion or offsetting road is notnecessarily precisely the same, especially for small positive andnegative contours (e.g., for a 3 mm diameter feature, the length of theperimeter road vs. a companion road may differ by 25 or 30%, while at 30mm the length of the companion road may be 5% or less difference). Insuch a case an amount of overlap determined according to the differencein perimeter lengths may be effective at removing twist.

For raster fill within the shells or walls, a twisting effect from therelaxation of residual stress may not be as pronounced because rasterrows may include some retrograde paths. However, as the filled interiorarea becomes smaller, differences in path length among raster rows andturns may be more pronounced. Overlap determined according to adifference in directional lengths (e.g., including straight rows as wellas end-of-row turns) may be used to offset a length difference. Inaddition, raster-like or cellular patterns may be printed in tilepatterns that each include main paths and parallel retrograde paths torelieve twisting stress relaxation within the tile and/or among tiles.

In one example of such an embodiment or expression of the invention, asshown in FIG. 36A, where deposition direction is shown with an arrowwithin a deposition path, a method for building a part with adeposition-based additive manufacturing system, may include depositing,in a first direction (as indicated by an internal arrow), apolymer-including material along a first contour tool path to form aperimeter path 371 of a layer of a green part and to define an interiorregion within the perimeter path. The material is also deposited in asecond direction retrograde the first direction on a second contour toolpath to form an adjacent path 372 in the interior region adjacent theperimeter path 371. The deposition of the adjacent path 372 in thesecond direction stresses polymer chains in the material in a directionopposite to stresses in polymer chains in the material in the perimeterpath 371, and reduces part twist caused by relaxation of the polymerchains in the part.

FIG. 36B may be considered a different version of the layer of FIG. 36A,or may be considered to depict an adjacent layer (FIG. 36B is depicted asmaller outer perimeter than FIG. 36A, such as would be the case for anadjacent layer sloping to a peak). As shown, an adjacent perimeter path376 in an adjacent layer may be alternatively or also deposited in aretrograde direction with respect to the perimeter path 371, and otherpaths such as raster fill 378 or honeycomb infill 377 may also beprinted in a retrograde direction with respect to parallel paths in anadjacent layer 374, 373 respectively. Also as shown in FIG. 36B, anadjacent road or deposition 376 may be deposited wider or at a higherrate than a perimeter path 375 (or narrower). When an odd number ofwalls is deposited at a perimeter, the changed width or deposition ratemay offset the twist tendency of two adjacent depositions (on eitherside) in the same layer.

While a butt joint as shown in FIG. 37B or 37J is one of the simplestseams (e.g., butt joints in adjacent roads or depositions may bealigned, rotationally offset, or in distant rotational positions), oneof a start of deposition or a stop of deposition to be located withinthe interior region of the layer as shown in FIG. 37A, or 37C through37H. As shown in FIGS. 37A through 37H, the locations of the start pointand the stop point may be configured to define various joints, overlapsand interlocks. As shown in FIGS. 37H and 37J, a contour tool pathbetween a path's start point and the stop point may define a raster paththat at least partially fills the interior region.

In another example of such an embodiment or expression of the invention,as shown in FIGS. 36A-36B, 37A-37H, and 37J, in building a part with adeposition-based additive manufacturing system having a deposition headand a controller 20, a first tool path for a layer of the part may bereceived by the controller, the received first tool path including aperimeter contour segment 371. A second tool path 372 may be receive fora layer of the part by the controller, including an interior regionsegment adjacent the perimeter contour segment. The deposition head maybe moved (including directed movement of a beam or ray of light orelectromagnetic energy) in a pattern that follows the perimeter contoursegment of the received first tool path to produce a perimeter path 371of a debindable composite including sinterable powder, and in a patternthat follows the interior region segment of the received second toolpath to produce an interior adjacent path 372 of the debindablecomposite, wherein the perimeter path 371 and the adjacent path 372 aredeposited in retrograde directions so that directions of residual stresswithin a binder of the debindable composite are opposite in theperimeter path and the adjacent path. As shown in FIGS. 37A-37H and 37J,this may also apply between adjacent layers, where the adjacent path 376is in an adjacent layer.

In another example of such an embodiment or expression of the invention,as shown in FIGS. 36A-36B, 37A-37H, and 37J, in building a part with adeposition-based additive manufacturing system, a digital solid modelmay be received for the part (e.g., a 3D mesh such as an STL file or a3D solid such as a NURBS, parasolid, IGES file). The digital solid modelmay be sliced (by, e.g., a computer or a cloud-based computing service)into a plurality of layers. A perimeter contour tool path 371 may begenerated based upon a perimeter of a layer of the plurality of layers,wherein the generated perimeter contour tool path defines an interiorregion of the layer. An interior adjacent path 372 may be generatedbased on the perimeter contour tool path within the interior region. Adebindable composite may be deposited including sinterable powder in afirst direction based on the perimeter contour tool path to form aperimeter 371 of the debindable composite for the layer. The debindablecomposite may be extruded in a second direction based on the perimetercontour tool path to form an interior adjacent path 372 of thedebindable composite for the layer. The deposition of the perimetercontour tool path 371 and the interior adjacent path 372 may be tracedin retrograde directions to one another so that directions of residualstress within a binder of the debindable composite are opposite in theperimeter contour tool path 371 and the interior adjacent path 372.Optionally, as shown in FIGS. 37A and 37C-37H, a start point of theperimeter contour tool path 371 and a stop point of the perimetercontour tool path 371 may be adjusted to locations within the interiorregion.

In another example of such an embodiment or expression of the invention,as shown in FIGS. 36A-36B, 37A-37H, and 37J, building a part with adeposition-based additive manufacturing system having a deposition headand a controller may include receiving a first tool path for a layer ofthe part by the controller, wherein the received first tool pathcomprises a contour segment. A second tool path may be received for alayer of the part by the controller, and wherein the received secondtool path overlaps the first tool path over more than 70 percent,preferably at least 90 percent of a continuous deposition length of thesecond tool path. The deposition head may be moved in a pattern thatfollows the first tool path to produce a perimeter path 371 of adebindable composite for the layer, and also moved in a pattern thatfollows the second tool path in a retrograde direction to the first toolpath to produce a stress-offsetting path 372 adjacent the perimeter pathof debindable composite. Directions of residual stress within a binderof the debindable composite may be opposite in the perimeter path 371and the stress-offsetting path 372.

Optionally, the second tool path may be continuously adjacent or overlapthe first tool path within the same layer, and may include interiorregion path within the same layer. Alternatively, or in addition, thesecond tool path is continuously adjacent over at least 90 percent ofthe first tool path within an adjacent layer, and may include aperimeter path of the adjacent layer.

In another example of such an embodiment or expression of the invention,as shown in FIGS. 36A-36B, 37A-37H, and 37J, in a method for building apart with a deposition-based additive manufacturing system having adeposition head and a controller, the method includes generating a toolpath with a computer. Instructions may be generated for the generatedtool path to the controller. A debindable composite may be depositedfrom the deposition head while moving the deposition head along thegenerated tool path to form a perimeter path of a layer of the part. Asshown in FIG. 37G, the perimeter path may include a first contour roadportion 378, and a second contour road portion 379, each of the firstcontour road portion and the second contour road portion crossing oneanother with an even number of X-patterns, forming an even number ofconcealed seams for the layer.

In another example of such an embodiment or expression of the invention,as shown in FIGS. 36A-36B, 37A-37H, and 37J, a deposition-based additivemanufacturing system having a deposition head and a controller may movethe deposition head along a first tool path segment 380 to form aperimeter road portion 371 for a layer of the part. As shown in FIG.37C, the deposition head may be moved along a direction changing toolpath segment 381; and moved along a second tool path segment 382 to forma stress-balancing road portion 372 adjacent to the perimeter roadportion 371. As shown in FIG. 37C, the direction changing tool pathsegment 381 may include a reflex angle continuation (e.g., between 180and 360 degrees) between the first tool path segment 380 and the secondtool path segment 382 within the same layer.

As shown in FIGS. 38A, 38B, 39A, 39B, and 40 nozzle structure can beused to improve printing properties of the metal powder compositefeedstocks discussed herein. Metal powder composite feedstocks such asMIM (Metal Injection Molding) feedstocks, are a composite material, asdiscussed herein, including sinterable metal powder and a binder, may bedesigned to facilitate MIM-specific processes. As discovered by variousauthors in the last twenty years, certain feedstocks can be adapted forextrusion-type 3D printing, e.g., Fused Deposition Modeling or FusedFilament Fabrication (“FDM” or “FFF”, terms for generic extrusion-type3D printing). Traditional extrusion feedstocks are not formed in thesame manner as MIM feedstocks, and include thermoplastic material thatmelts or softens. In the case of MIM feedstocks, other materialsintended for injection molding or the green-to-brown part process areoften included in the feedstock—typically waxes, but including other lowmelting point and low viscosity materials. The higher viscosity (vs.lower viscosity of wax-including MIM feedstocks) and lower thermalconductivity (vs. high metal powder content of MIM feedstocks) ofFDM/FFF thermoplastic filament may require a larger melt zone to get thematerial to a suitable temperature and thus suitable viscosity to flow.

If the melting point is low enough, or the material reactive enough,small bubbles or other discontinuities can form in the fluidizedfeedstock during the extrusion process when using ordinaryextrusion-type nozzles, heat breaks, and heating. The bubbles createprinting problems in several ways—for example, uneven printing in bothgaps and drips, or uneven printing of adjacent roads or roads indifferent parts of the layer or part. The present disclosure provides asolution specifically for promoting even printing. Bubbles may be formedin many ways—for example gas dissolution from the solid phase, i.e.small amounts of moisture making steam. Alternatively, or in addition,micro bubbles may coalesce in the nozzle that entered the feedstockfilament in a feedstock manufacturing phase—e.g., bubbles in pelletmaterial converted into filament that are not removed during thisprocess, or bubbles introduced during filament production.Alternatively, or in addition, air may be pulled into the system duringa retract step following steady printing (an extrusion type 3D printermay be set to “retract”, i.e., reverse the filament drive direction, bya small amount—e.g., 1-5 mm—following steady printing or during anon-printing nozzle translation to relieve pressure in the melt zone).In addition, or in the alternative, bubbles may be caused by deformationdue to the filament extruder hob (e.g., caused by any of grabbing teeth,pressure, or heating)

An additional benefit of the present system is decreasing the volume ofmelt for a practically sized heater block and nozzle system, providingmore responsive extrusion control. Additional back pressure may alsogive better extrusion control given the very low viscosity of some MIMmaterials. In one implementation, for example for a MIM material whichbegins to melt or liquefy at around 130-150 C, the material may beheated in the print head to 180-230 C to promote adhesion. In thisalternative, instead of reducing the volume of the melt zone using along, thin melt channel (e.g., 1:10 width-height aspect ratio fordiameter and a volume of 20 mm{circumflex over ( )}3, the melt zone maybe a short 1:2 aspect ratio and a volume of 20 mm{circumflex over( )}3—e.g., 3 mm of melt zone height, 1.5 mm of melt zone diameter. Thelonger, thin melt channel however allows more heating length forexposure to a heating element (e.g., as shown in the Figures, a shortmelt zone cannot necessarily accommodate a large and powerful heatingcartridge). A reduced filament diameter (e.g. instead of a customary 3mm or 1.75 mm, a 1 mm diameter filament) may permit a smaller bendradius for a given temperature, and better control over an amountextruded—for a given step size on the extruder, less material isextruded.

With respect to advised or advantageous dimensions, below a 10:1 nozzleto particle diameter ratio jamming may begin. Jamming is exacerbated byless spherical particles (e.g., platelets or flakes, which can becreated during mixing or screw extrusion). Traditional MIM (or CIM)materials may be between 55% and 65% metal (or ceramic) powder loadingby volume, but at this level of loading, separation layer material insmall powder sizes (e.g., less than 1 um diameter) of alumina ceramicmay tend to sinter at steel sintering temperatures. As the size ofpowder increases slightly to 2 um, the separation layer may becomechalk-like. Accordingly, 15-35% powder by volume with a powder diameterof 5 um or higher for alumina or similar ceramic powder loaded in a MIMbinder (e.g., wax-polyethylene, as discussed herein) may perform well asa separation layer. Alternatively, 10-20% powder by volume with a powderdiameter of 2 um or lower (or 1 um or lower) for alumina or similarceramic powder loaded in a MIM binder may perform well as a separationlayer. Further, these may be combined (e.g., some particles smaller than1 um and some particles larger than 5 um).

A conventional FDM/FFF filament or melt chamber may be approximately1.7-3 mm, and in the present invention the melt chamber may be 0.6-1 mmin diameter for a tip outlet diameter of 0.1-0.4 mm (for a filamentdiameter of 1.0-2 mm). The volume of the melt chamber (the heatedsubstantially cylindrical chamber of constant diameter extending fromadjacent the nozzle tip to a melt interface) the may be approximately15-25 mm{circumflex over ( )}3 vs. a melt chamber in conventionalFDM/FFF of approximately 70 mm{circumflex over ( )}3.

As shown in FIGS. 38A and 38B, an FDM/FFF nozzle assembly may include anozzle 38-1 including part of the cylindrical melt chamber 38-2 having alarger diameter and a transition to the nozzle outlet 38-3. Thetransition may be smooth (tapered 38-4, as in FIG. 38A) or stepped 38-5(as in FIG. 38B). Both the nozzle 38-1 and a heat break 38-5 aretightened (e.g., screwed) into a heater 38-6 block to abut one another,the heat break 38-5 including the remainder of the cylindrical meltchamber. The heat break 38-5 includes a narrow waist made of a lowerheat conductivity material (e.g., stainless steel) to provide the meltinterface via a sharp temperature transition between the top portion ofthe heat break 38-5 (which is cooled via the heat sink) and the lower,conductively heated portion of the heat break 38-5. The melt interfacebetween the solid filament 38-8 and the liquefied material in the meltchamber 38-2 is typically near the narrow waist (adjacent above orbelow, or within). As shown in each of FIGS. 38A and 38B, an FDM/FFFnozzle assembly may include a melt chamber of approximately 1.8 mmdiameter and 10 mm height, a volume of about 70 mm{circumflex over( )}3, vs. a nozzle outlet of approximately 0.25-0.4 mm diameter. Asshown, a cartridge heater 38-6 (in FIG. 38A) or a coiled inductiveheater 38-6 (in FIG. 38B) are suitable. As shown, in some cases a PTFEinsert 38-9 may provide resistance to filament jamming.

As shown in FIGS. 39A and 39B, a MIM material extrusion nozzle assemblymay be structurally similar—e.g., with a smooth or stepped transition inthe nozzle 39-1, a heat break 39-5 including a narrow waist, and othercomponents as previously described (e.g., with reference numbers 39-#corresponding to numbers 38-# previously employed). A solid-statePeltier cooler may be used on or adjacent the heat break 39-5, and maybe adhered to the heat break 39-5 by heat transfer cement or other highheat conductivity interface. As shown in each of FIGS. 39A and 39B, aMIM material extrusion nozzle assembly may include a melt chamber 39-2of approximately 0.6-1 mm diameter and 10 mm height, a volume of about20 mm{circumflex over ( )}3, vs. a nozzle outlet 39-3 of approximately0.1-0.4 mm diameter. As shown in FIG. 39B, a narrowing insert 39-11 maybe used to convert an FDM nozzle for MIM material extrusion (e.g., themelt chamber volume vs. nozzle outlet size or filament relationshipsdescribed herein are related to MIM material dimensions duringextrusion, not necessarily the specific nozzle, heat break, or insertparts). As shown in FIG. 40, a MIM material extrusion nozzle assemblymay include a melt chamber 39-2 of approximately 1.7-3 mm diameter and1-4 mm height, a volume of about 20 mm{circumflex over ( )}3, vs. anozzle outlet of approximately 0.1-0.4 mm diameter.

With respect to the binder jetting example shown in FIG. 1B, in all ofthe preceding examples in which an extruder using filament is notrequired, the binder jetting example printer 1000J and associatedprocesses may be used. In a 3D printer for making desired 3D greenparts, a binder may be jetted as a succession of adjacent 2D layershapes onto a sinterable metal or ceramic powder bed in successivelayers of powder feedstock, the powder bed being refilled with new orrecycled feedstock and releveled/wiped for each successive layer. The 3Dshape of the desired 3D green part and associated sintering supports orunderlying shrinking platform (for holding unsupported spans of the 3Dgreen part in place vs. gravity during sintering and maintaining anoverall shape of the 3D green part) are built up as a bound compositeincluding the sinterable powder and the binder, embedded in a volume ofloose powder. The 3D green part and its sintering supports will later bedebound and then sintered, and the sintering supports removed.

In some layers, differing amounts of binder may be jetted depending onwhether a 2D layer shape segment being formed is an external wall,internal wall, or honeycomb wall, or internal bulk material (ordepending on the printing location relative to such perimeters orareas). This results in differing (optionally a continuous or stepwisegradient) of volume fraction proportions of binder to powder, e.g., from90% binder to 100% powder through 50:50 up to 10% binder to 90% powder.For example, a higher volume fraction of binder may be located on anouter shell (and/or inner shell), progressively reducing inward toward,e.g., area centroids.

In some layers, a release material (including another powder that doesnot sinter at the sintering temperature of the feedstock powder) mayalso be applied in a complementary 2D shape (e.g., jetted in a binder,extruded in a binder) for example, intervening between a support shapein a lower layer and a part shape in a layer two above.

In some layers, placeholder material (without either the green partpowder or the release material powder) may also be applied in acomplementary 2D shape of desired free space within the green partand/or sintering supports (e.g., jetted or extruded). In some layers,the placeholder material may also or alternatively be applied in a wallor “mold” shape, e.g., occupying external free space to the part shape,capturing unbound sinterable powder inside the mold shape. In otherwords, an external shell (e.g., wax) may be formed of the placeholdermaterial. The external shell 2D shapes are deposited in each candidatelayer on top of the preceding powder (e.g., bound powder, unboundpowder, and/or release material) layer, then a subsequent layer ofunbound powder feedstock is wiped on. As shown in FIG. 1B, a doctorblade 138 may be used to slice the top of the 2D shell shape off(leveling) or a silicon roller/blade 138 may be used to slice the top ofthe 2D shell shape off—the silicon roller/blade may accept somedeformation, e.g., deform to accommodate the bump of the plastictolerance above the printing plane.

The binder may be jetted into roofs, floors, lattice, honeycomb, orskeletal reinforcement shapes within the mold shape (e.g., startingspaced away from the mold shape) to help hold the unbound sinterablepowder versus gravity, or mechanical disturbance during downstreamprocesses such as leveling or moving the part from station to station.For example, in some 2D layers, an internal holding pattern such ashexagon, triangle, or as previously describe lower density or highvolume fraction of binder may be used as a holder, in combination witheither an outer shell formed from bound composite, an outer shell formedfrom high volume fraction binder bound composite (e.g., 70% binder),and/or a mold shape formed from the placeholder material. As noted, thismay help prevent motion of parts during printing/or during layerre-application.

Further, in some layers, the placeholder material may also oralternatively be applied in a complementary 2D shape of adhesivebetween, e.g., the shrinking platform formed from bound powder and theunderlying build platform, or between a plurality of adjacent or stacked3D green parts and associated sintering supports to allow multiple partsto be built up per run. The adhesive function may, again, help hold theany of the shapes versus mechanical disturbance during downstreamprocesses such as leveling or moving the part from station to station.It should be noted that the binder jetting into sinterable powder mayalso be used to form adhering tacks as described herein between theshrinking platform and build platform, as well as or alternativelybetween a plurality of adjacent or stacked 3D green parts and associatedsintering supports. In other words, the part may be anchored part with(e.g., solvent removed) binder to a ground plane (e.g., build plate)and/or parts to each other (e.g., in the Z axis, when printing one ontop of another).

After each layer, the powder bed is refilled and releveled/wiped (with adoctor blade 138, roller, wheel or other powder leveling mechanism)flush with the green part shape, the release material shape, and/or thefree space placeholder material shape. Optionally, a surface finishingmechanism flattens or shapes (rolling, shaving, ironing, abrading,milling) a recent or a most recent layer of green part shape, releasematerial shape, and/or placeholder material shape before the powder bedis refilled about them.

The 3D shapes of each of the green part, sintering supports, interveningrelease material, and placeholder free space material are built up insuccessive layers, and in 3D space may take essentially any interlocking3D forms. In many cases, the green part is formed as a recognizable 3Dobject, with separation material forming planes, arches, hemispheres,organic shapes or the like separating the 3D object from columns ofsintering supports below, leading down to a shrinking platform asdescribed herein, which is adhered to a build platform via placeholdermaterial and/or bound composite tacks. Optionally, as described, withinthe recognizable 3D object, desired free space may be filled withplaceholder material and/or unbound sinterable powder. Among theplaceholder material and/or unbound sinterable powder may be depositedbound composite honeycomb or lattice or the like containing orentraining either or both of the placeholder material or unboundsinterable powder. Optionally, as described, about the recognizable 3Dobject, a mold shape defining the outer skin of the 3D object may beformed of the placeholder material. Additionally, or in the alternative,a skin shape forming the outer skin of the 3D object may be formed ofthe bound composite.

Subsequently, the 3D green part(s) together with sintering supports,release shapes, and placeholder or adhesive shapes is removed from thepowder, and cleaned of remaining unbound powder. Unbound powder may beremoved from the surroundings of the 3D green part(s) and sinteringsupports via outlets formed in the bound composite, or left entrainedwithin the desired green part. Subsequently, the green part and itssintering supports may be handled as otherwise described in thisdisclosure. Bound composite outer and inner walls and internal honeycombwalls will be debound as described to form the brown part assembly.Release material will be debound as described, become separation powderfor removing the sintering supports, and is retained for sintering andremoved following sintering. Placeholder material may be debound(including in a solvent, catalytic, or thermal process) or even, if adifferent material from the binder, removed before or after debinding.In some cases, high temperature placeholder material that retains itsshape at high heat but may be disassembled by further vibration,mechanical, radiation, or electrical processing (e.g., carbon or ceramiccomposite) may be retained through sintering.

Alternatively, the debinding step may not be necessary, for the greenpart shape and/or sintering supports if a single stage binder can bepyrolysed in a sintering furnace. In such a case, the green partassembly is taken directly to the furnace. Bound composite outer andinner walls and internal honeycomb walls are debound and sintered in anintegrated process. Release material may be debound prior to theintegrated debinding and sintering in the furnace, or at may be deboundin the furnace as well. Placeholder material may be debound (includingin a solvent, catalytic, or thermal process) prior to the integrateddebinding and sintering in the furnace, or at may be debound in thefurnace as well.

A material may be supplied (pellet extruded, filament extruded, jettedor cured) containing a removable binder as discussed herein (two or onestage) and greater than 50% volume fraction of a powdered metal having amelting point greater than 1200 degrees C. (including various steels,such as stainless steels or tool steels). The powdered metal may havewhich more than 50 percent of powder particles of a diameter less than10 microns, and advantageously more than 90 percent of powder particlesof a diameter less than 8 microns. The average particle size may be 3-6microns diameter, and the substantial maximum (e.g., more than the spanof +/−3 standard deviations or 99.7 percent) of 6-10 microns diameter.

Smaller, e.g., 90 percent of less than 8 microns, particle sizes maylower the sintering temperature as a result of various effects includingincreased surface area and surface contact among particles. In somecases, especially for stainless and tool steel, this may result in thesintering temperature being within the operating range of a fused tubefurnace using a tube of amorphous silica, e.g., below 1200 degrees C.Smaller diameter powder material may be additively deposited insuccessive layers to form a green body as discussed herein, and thebinder removed to form a brown body (in any example of deposition and/ordebinding discussed herein).

Definitions

A “sintering temperature” of a material is a temperature range at whichthe material is sintered in industry, and is typically a lowesttemperature range at which the material reaches the expected bulkdensity by sintering, e.g., 90 percent or higher of the peak bulkdensity it is expected to reach in a sintering furnace.

“Honeycomb” includes any regular or repeatable tessellation for sparsefill of an area (and thereby of a volume as layers are stacked),including three-sided, six-sided, four-sided, complementary shape (e.g.,hexagons combined with triangles) interlocking shape, or cellular.“Cells” may be vertical or otherwise columns in a geometric prism shapeakin to a true honeycomb (a central cavity and the surrounding wallsextending as a column), or may be Archimedean or other space-fillinghoneycomb, interlocking polyhedra or varied shape “bubbles” with acentral cavity and the surrounding walls being arranged stacked in alldirections in three dimensions. Cells may be of the same size, ofdiffering but repeated sizes, or of variable size.

“Extrusion” may mean a process in which a stock material is pressedthrough a die to take on a specific shape of a lower cross-sectionalarea than the stock material. Fused Filament Fabrication (“FFF”),sometimes called Fused Deposition Manufacturing (“FDM”), is an extrusionprocess. Similarly, “extrusion nozzle” shall mean a device designed tocontrol the direction or characteristics of an extrusion fluid flow,especially to increase velocity and/or restrict cross-sectional area, asthe fluid flow exits (or enters) an enclosed chamber.

“Shell” and “layer” are used in many cases interchangeably, a “layer”being one or both of a subset of a “shell” (e.g., a layer is an 2.5Dlimited version of a shell, a lamina extending in any direction in 3Dspace) or superset of a “shell” (e.g., a shell is a layer wrapped arounda 3D surface). Shells or layers are deposited as 2.5D successivesurfaces with 3 degrees of freedom (which may be Cartesian, polar, orexpressed “delta”); and as 3D successive surfaces with 4-6 or moredegrees of freedom.

In the present disclosure, “3D printer” is inclusive of both discreteprinters and/or toolhead accessories to manufacturing machinery whichcarry out an additive manufacturing sub-process within a larger process.A 3D printer is controlled by a motion controller 20 which interpretsdedicated G-code and drives various actuators of the 3D printer inaccordance with the G-code. “Fill material” includes composite materialformed of a debindable material and a sinterable powder, e.g., beforedebinding.

“Fill material” includes material that may be deposited in substantiallyhomogenous form as extrudate, fluid, or powder material, and issolidified, e.g., by hardening, crystallizing, or curing. “Substantiallyhomogenous” includes powders, fluids, blends, dispersions, colloids,suspensions and mixtures.

“3D printer” meaning includes discrete printers and/or toolheadaccessories to manufacturing machinery which carry out an additivemanufacturing sub-process within a larger process. A 3D printer iscontrolled by a motion controller 20 which interprets dedicated G-code(toolpath instructions) and drives various actuators of the 3D printerin accordance with the G-code.

“Deposition head” may include jet nozzles, spray nozzles, extrusionnozzles, conduit nozzles, and/or hybrid nozzles.

“Filament” generally may refer to the entire cross-sectional area of a(e.g., spooled) build material.

“Sintering” as used herein may mean full or partial sintering. Wherefull sintering includes sintering a material to 94% density or higher,and partial sintering includes the onset of micro-necking betweenparticles whereby the material no longer resembles a free-flowingpowder, and up to 94% density.

“Flake” is distinct from a “powder” in that it has been heated to atemperature sufficient to initiate sintering which is defined above asthe onset of necking between particles. This can be visualized by SEM ormicroscope imaging where a powder's can be seen as distinct spheres orparticle shapes, while a flake would be composed of a number of powdersthat have necked together. Another way to distinguish between the two isto disperse the material in a compatible solvent to create a colloidalsuspension. The powder material should be capable of being sievedthrough an appropriately sized filter (for example a powder with the PSDof D90-10 um should pass through a mesh filter with between 10-20 umsized opening) while flakes or sintered powder will not be able to passthrough the same filter.

What is claimed is: 1-28. (canceled)
 29. A method of additivelymanufacturing an object, the method comprising: depositing a compositeincluding a metal particulate filler and a debindable matrix insuccessive layers to form a densification linking platform,densification linking supports, and a densification linking part, atleast a portion of the successive layers of the object having at leastone wall substantially enclosing an interior volume of a part; forming adebinding acceleration structure having interconnected chambers and aplurality of access channels that penetrate one or more of the at leastone wall exposing the composite, such that when exposed to a fluiddebinder during a debinding process, the exposed composite forms a brownpart including the debound densification linking platform, the debounddensification linking supports, and the debound densification linkingpart; debinding the composite including penetrating the fluid debinderinto the debinding acceleration structure through the plurality ofaccess channels to debind the matrix from within the interior volume ofthe densification linking platform, the densification linking supports,or the part; and sintering, during a sintering process, the brown partassembly to densify at a rate substantially common throughout the brownpart assembly to form the object.
 30. The method of claim 29, furthercomprising connecting a portion of the plurality of access channels to apressurized supply of debinding fluid to force debinding fluid throughthe portion of the plurality of access channels.
 31. The method of claim29, wherein the step of forming the interconnected chambers and theplurality of access channels that penetrate the one or more of the atleast one wall exposing the composite of the debinding accelerationstructure comprises fluidly interconnecting a plurality of honeycombcavities.
 32. The method of claim 29, further comprising forming thedebinding acceleration structure in additive layers, wherein at leastone of the plurality of access channels spans a plurality of theadditive layers.
 33. The method of claim 29, further comprising:depositing one or more part release layers between the densificationlinking supports and the part with a release composite comprising aceramic particulate filler and a binder; and forming a routing channelthrough the part release layer and to at least one of the plurality ofaccess channels that permits the fluid debinder to flow through the oneor more part release layers to the densification linking supports. 34.The method of claim 29, wherein the step of debinding comprisescyclically filling and draining the debinding acceleration structureusing a fluid debinder, thereby repeatedly immersing the densificationlinking platform, the densification linking supports, and the part, aswell as filling and draining the interconnected chambers, to form thebrown part assembly.
 35. The method of claim 29, wherein the step ofdebinding comprises holding the densification linking platform, thedensification linking supports, and the part immersed in the debindingchamber for a dwell time that permits the fluid debinder to flow throughthe plurality of access channels.
 36. The method of claim 29, whereinthe step of debinding comprises penetrating the fluid debinderthroughout the interconnected chambers to debind the matrix from withinthe interconnected chambers.
 37. The method of claim 29, whereininterconnections between the interconnected chambers have a crosssectional area of less than 1% of a surface area of the interior volumeof the densification linking platform, the densification linkingsupports, or the part.
 38. The method of claim 29, wherein depositingthe composite in successive layers to form the debinding accelerationstructure comprises depositing the composite within the interior volumeof the densification linking supports connected to lateral sides of thepart.
 39. A method of additively manufacturing an object, the methodcomprising: receiving, by a controller, a first tool path for a firstlayer of a part, wherein the received first tool path comprises aperimeter contour segment in the first layer; receiving, by thecontroller, a second tool path for a second layer of the part, whereinthe received second tool path comprises a parallel segment adjacent tothe perimeter contour segment; depositing a composite comprising apolymer-based matrix and a powdered sinterable metal in a pattern thatfollows the perimeter contour segment of the received first tool path toproduce a perimeter path of the composite; depositing the composite in apattern that follows the parallel segment of the received second toolpath in a retrograde direction with respect to the perimeter path toproduce a stress-offsetting adjacent path of the composite, depositingthe composite in a pattern that follows the parallel segment of thereceived second tool path to produce a stress-offsetting retrogradeadjacent path of the composite, wherein the perimeter path and thestress-offsetting adjacent path are deposited in retrograde directionswith respect to one another such that directions of residual stresswithin the polymer-based binder of the composite are opposite in theperimeter path and the stress-offsetting retrograde adjacent path. 40.The method of claim 39, wherein stresses within the stress-offsettingadjacent path are continuously adjacent to, parallel to, and opposite toat least 90 percent of stresses within the perimeter path.
 41. Themethod of claim 39, further comprising debinding the polymer-basedmatrix sufficient to form a shape-retaining brown part.
 42. The methodof claim 41, further comprising sintering the shape-retaining brown partto densify the part as neighboring metal particles throughout theshape-retaining brown part undergo atomic diffusion, wherein thedeposition of the composite positions residual stresses within thepolymer-based binder in opposing directions in the perimeter path andthe stress-offsetting adjacent path and reduces part twist caused bystress and relaxation of polymer chains in the composite.
 43. The methodof claim 39, wherein the second tool path is continuously adjacent toand parallel to at least 90 percent of a length of the first tool pathwithin an adjacent layer.
 44. The method of claim 39, further comprisingdepositing the composite in a pattern along a direction changing toolpath segment, wherein the direction changing tool path segment is areflex angle continuation joining the first tool path and the secondtool path within a same layer.
 45. The method of claim 39, furthercomprising depositing the composite to form sintering supports below thepart.
 46. The method of claim 39, further comprising forming one or morerelease layers of a release composite including a ceramic particulatefiller and a binder between the part and the sintering supports.
 47. Themethod of claim 39, wherein the step of debinding the polymer-basedmatrix sufficient to form the shape-retaining brown part comprisesdebinding the polymer-based matrix of the part and the sinteringsupports.
 48. The method of claim 46, further comprising debinding thebinder of the one or more release layers, thereby allowing a ceramicparticulate that facilitates release of the part from the sinteringsupports to remain; and sintering, during a sintering process, the partand the sintering supports to densify at a rate substantially commonthroughout and to powderize the one or more release layers.
 49. Themethod of claim 48, further comprising forming a densification linkingplatform of the composite beneath the part and the sintering supports.50. The method of claim 39, further comprising tacking the densificationlinking platform to the part at a plurality of positions dispersed aboutan exterior of the part to substantially counteract a friction forcebetween the shape-retaining brown assembly and a surface beneath thedensification linking platform.
 51. The method of claim 49, whereinforming the densification linking platform comprises forming thedensification linking platform to be horizontally larger than the partand having a cross-sectional area with no concavities.
 52. The method ofclaim 49, wherein forming the densification linking platform comprisesforming the densification linking platform having a horizontal planelarger than a largest horizontal plane of the part.
 53. The method ofclaim 49, wherein forming the densification linking platform comprisesforming the densification linking platform having a cross-sectional areawith a convex shape.
 54. The method of claim 53, wherein forming thedensification linking platform comprises the forming the densificationlinking platform having the cross-sectional area with the convex shapebeing a polygon substantially free of concavities.
 55. The method ofclaim 52, wherein forming the densification linking platform comprisesforming the densification linking platform having a cross-sectional areahaving a centroid aligned with that of the part above.
 56. The method ofclaim 52, further comprising forming a sliding release layer below thedensification linking platform of equal or larger surface area than abottom of the densification linking platform that reduces lateralresistance between the densification linking platform and a surfacebeneath the densification linking platform.
 57. The method of claim 39,further comprising forming separable interconnected sintering supportsto a side of the part by forming separable attachment protrusions of thecomposite between the sintering supports and the side of the part. 58.The method of claim 57, further comprising connecting the interconnectedsintering supports to the densification linking platform usingconnections of the composite of greater cross-sectional area than theseparable attachment protrusions.
 59. The method of claim 39, furthercomprising forming soluble support structures including a solublebinder, the soluble support structures resisting downward forces duringthe forming of the part.
 60. The method of claim 59, further comprising,prior to sintering the shape-retaining brown part assembly, debindingthe soluble binder of the soluble support structures.
 61. The method ofclaim 39, further comprising: forming a lateral support shell of thecomposite following at least a portion of a lateral contour of the part;and connecting the lateral support shell to the lateral contour of thepart by forming separable attachment protrusions of the compositebetween the lateral support shell and the part.
 62. The method of claim48, further comprising separating the part from the sintering supportsalong the powderized one or more release layers.
 63. A method ofadditively manufacturing an object, the method comprising: forming adensification linking platform comprising successive layers of acomposite, the composite comprising a metal particulate filler in apolymer-based binder matrix; forming densification linking supports ofsuccessive layers of the composite above the densification linkingplatform; forming a part of successive layers of the composite on thedensification linking platform and densification linking supports;depositing the composite along wall and infill toolpaths forming atleast one walled structure having an internal volume in which infillstructures are provided for one or more of the platform, supports, andpart, at least a portion of the wall tool paths forming a plurality ofaccess channels penetrating through the at least one walled structuresinto the internal volume.
 64. The method of claim 63, further comprisingdebinding the polymer-based binder matrix by flowing a fluid debinderaround the densification linking platform, the densification linkingsupports, and the part through the plurality of access channels.
 65. Themethod of claim 64, wherein the step of debinding is sufficient to forma shape-retaining brown part assembly comprising a debound densificationlinking platform, debound densification linking supports, and a deboundpart.
 66. The method of claim 65, further comprising sintering theshape-retaining brown part assembly to densify the densification linkingplatform, the densification linking supports, and the part together at asame rate as neighboring metal particles throughout the shape-retainingbrown part assembly undergo atomic diffusion.
 67. The method of 63,further comprising interconnecting the densification linking supports toa side of the part by forming separable attachment protrusions of thecomposite between the densification linking supports and the side of thepart.
 68. The method of 63, further comprising forming a lateraldensification linking support shell of the composite comprising forminga lateral contour of the part.
 69. The method of claim 68, furthercomprising connecting the lateral contour of the part by formingseparable attachment protrusions of the composite between the lateraldensification linking support shell to the part.
 70. The method of 63,further comprising forming soluble support structures of a solublebinder, the soluble support structures resisting downward forces duringthe forming of the part.
 71. The method of 63, further comprising, priorto sintering the shape-retaining brown part assembly, debinding thematrix sufficient to form a shape-retaining brown part assemblycomprising the densification linking platform, the densification linkingsupports, and the part; and debinding the soluble binder of the solublesupport structures.
 72. The method of 63, further comprising forming oneor more part release layers between the densification linking supportsand the part with a release composite comprising a ceramic particulatefiller and a binder.
 73. The method of claim 72, further comprisingmaintaining the one or more part release layers and shape-retainingbrown part assembly as a unit during the debinding and during thesintering.
 74. The method of claim 73, further comprising aftersintering, separating the one or more part release layers, thedensification linking platform, and the densification linking supportsfrom the part.
 75. The method of 63, further comprising forming aplurality of distribution channels among the infill toolpaths.
 76. Themethod of claim 75, wherein a portion of the distribution channels ofthe plurality of distribution channels fluidly interconnect pairs ofaccess channels.
 77. The method of claim 76, wherein a portion of thedistribution channels of the plurality of distribution channels fluidlyinterconnect portions of the internal volume.
 78. The method of claim77, wherein the portions of the internal volume comprise cells,cavities, and infill patterns.
 79. The method of claim 78, furthercomprising flowing the fluid debinder through the plurality of accesschannels, the plurality of distribution channels, and the internalvolume to accelerate the debinding step.
 80. The method of claim 79,wherein flowing the fluid debinder further comprises releasing the flowof fluid debinder out through a portion of the plurality of accesschannels to accelerate the debinding.
 81. The method of 63, furthercomprising surrounding the densification linking platform, thedensification linking supports, and the part to accelerate thedebinding.
 82. The method of claim 81, further comprising draining andreplenishing a bath of the fluid debinder surrounding the densificationlinking platform, the densification linking supports, and the part toaccelerate the debinding.
 83. The method of claim 82, further comprisingdraining and replenishing a supply of the debinding fluid entering theportion of the plurality of access channels to accelerate fluid flowand/or debinding.
 84. The method of 63, wherein the step of depositingthe composite to form the densification linking platform, thedensification linking supports, and the part comprises forming adjacenttoolpaths including a first toolpath along a perimeter patterned pathand a second toolpath along a retrograde patterned path.
 85. The methodof claim 84, wherein depositing the composite comprises depositingadjacent tool paths in a same layer in retrograde directions.
 86. Themethod of claim 85, wherein a centroid of a combined densificationlinking platform and connected densification linking supports issubstantially aligned with a centroid of the part.